Blue emitting semiconductor nanocrystals and compositions and devices including same

ABSTRACT

A semiconductor nanocrystal capable of emitting blue light upon excitation. Also disclosed are devices, populations of semiconductor nanocrystals, and compositions including a semiconductor nanocrystal capable of emitting blue light upon excitation. In one embodiment, a semiconductor nanocrystal capable of emitting blue light including a maximum peak emission at a wavelength not greater than about 470 nm with a photoluminescence quantum efficiency greater than about 65% upon excitation. In another embodiment, a semiconductor nanocrystal includes a core comprising a first semiconductor material comprising at least three chemical elements and a shell disposed over at least a portion of the core, the shell comprising a second semiconductor material, wherein the semiconductor nanocrystal is capable of emitting blue light with a photoluminescence quantum efficiency greater than about 65% upon excitation. In a further embodiment, a semiconductor nanocrystal includes a core comprising a first semiconductor material comprising at least three chemical elements and a shell disposed over at least a portion of the core, the shell comprising a second semiconductor material comprising at least three chemical elements, wherein the semiconductor nanocrystal is capable of emitting light including a maximum peak emission in the blue region of the spectrum upon excitation.

This application is a continuation of U.S. patent application Ser. No.12/454,701 filed 21 May 2009, now U.S. Pat. No. 8,404,154, issued on 26Mar. 2013, which is a continuation of commonly owned PCT Application No.PCT/US2007/024305 filed 21 Nov. 2007, which was published in the Englishlanguage as PCT Publication No. WO 2008/063652 on 29 May 2008. The PCTApplication claims priority to U.S. Application Nos. 60/866,826, filed21 Nov. 2006, 60/866,840, filed 21 Nov. 2006, and 60/866,833, filed 21Nov. 2006. The disclosures of each of the foregoing applications arehereby incorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The technical field of the invention relates to semiconductornanocrystals and compositions and devices including same.

SUMMARY OF THE INVENTION

The present invention relates to a semiconductor nanocrystal capable ofemitting blue light upon excitation. The present invention also relatesto populations of semiconductor nanocrystals, devices and compositionsincluding semiconductor nanocrystal capable of emitting blue light uponexcitation.

In accordance with one aspect of the invention there is provided asemiconductor nanocrystal capable of emitting blue light including amaximum peak emission at a wavelength not greater than about 470 nm witha photoluminescence quantum efficiency greater than about 65% uponexcitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 70% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 80% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 90% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 95% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isabout 100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In certain embodiments the semiconductor nanocrystal can comprise afirst semiconductor material.

In certain embodiments, the semiconductor nanocrystal comprises acore/shell structure wherein the core comprises a first semiconductormaterial and a shell comprising a second semiconductor material whereinthe shell is disposed over at least a portion of a surface of the core.

For example, in the foregoing embodiments, the first semiconductormaterial can comprise one or more chemical elements. Non-limitingexamples of first semiconductor materials include compositions includinga chemical element from Group IVA and compositions represented by thegeneral formula MA wherein M comprises at least one chemical element andA comprises at least one chemical element. In certain embodiments, thefirst semiconductor material can comprise at least three or moredifferent chemical elements. Non-limiting examples of firstsemiconductor materials include compositions represented by the generalformula MA wherein M comprises at least one chemical element and Acomprises at least one chemical element. (This general formula does notrepresent the actual relative molar amounts of the various chemicalelements comprising the semiconductor material.) In certain otherexamples, M can comprise at least two different chemical elements and Acan comprise at least one chemical element or M can comprise at leastone chemical element and A can comprise at least two different chemicalelements. In certain examples, M comprises one or more elements fromGroup IA (for example, lithium, sodium, rubidium, and cesium), Group IIA(for example, beryllium, magnesium, calcium, strontium, and barium),Group IIB (for example, Zn, Cd, and Hg), Group MA (for example, B, Al,Ga, In, and Ti), Group IVA (for example, Si, Ge, Sn, and Pb), or thetransition metals (for example, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn,Tc, Re, Fe, Co, Ni, Pd, Pt, Rh, and the like). (See, F. A. Cotton etal., Advanced Inorganic Chemistry, 6th Edition, (1999). In certainexamples, A comprises one or more elements selected from Group VA (forexample, nitrogen, phosphorus, arsenic, antimony, and bismuth) and/orGroup VIA (for example, oxygen, sulfur, selenium, and tellurium). Othersemiconductor materials suitable for inclusion in the core, including,but not limited to, other examples disclosed in the detaileddescription, can be used. The first semiconductor material is preferablyan inorganic semiconductor material.

In certain embodiments, M comprises one or more chemical elements fromGroup IIA and/or Group IIB and A comprises one or more chemical elementsfrom Group VIA.

In certain embodiments, M comprises one or more chemical elements fromGroup IIA and/or Group IIB and A comprises one or more chemical elementsfrom Group VA.

In certain other embodiments, M comprises one or more chemical elementsfrom Group IIIA and A comprises one or more chemical elements from GroupVA.

In certain embodiments, M comprises one or more chemical elements fromGroup IVA and A comprises one or more chemical elements from Group VIA.

In certain embodiments, M comprises one or more chemical elements fromGroup IA and/or Group IIIA and A comprises one or more chemical elementsfrom Group VIA.

In certain embodiments, M comprises one or more chemical elements fromGroup IIA and/or Group IVA and A comprises one or more chemical elementsfrom Group VA.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and sulfur.

In certain embodiments, a first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1. In certain embodiments, 0<x≦0.5. Incertain embodiments, 0<x≦0.3. In certain embodiments, 0.05<x<0.2. Incertain embodiments, 0.1≦x≦0.15. In certain embodiments, x is from about0.10 to about 0.12.

In certain embodiments wherein x≧0.1, a maximum peak emission can occurat a wavelength not greater than about 470 nm.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain other embodiments, the first semiconductor material does notinclude an element from Group IIA.

In certain embodiments, the first semiconductor material can comprise analloy of three or more chemical elements.

In certain embodiments, the first semiconductor material can comprise ahomogeneous alloy of the three or more chemical elements.

In semiconductor nanocrystals comprising a core/shell structure, theshell comprises a second semiconductor material. For example, the secondsemiconductor material can comprise one or more chemical elements.Non-limiting examples of second semiconductor materials includecompositions including a chemical element from Group IVA andcompositions represented by the general formula M′A′ wherein M′comprises at least one chemical element and A′ comprises at least onechemical element. In certain embodiments, the second semiconductormaterial can comprise at least three or more different chemicalelements. Non-limiting examples of second semiconductor materialsinclude compositions represented by the general formula M′A′ wherein M′comprises at least one chemical element and A′ comprises at least onechemical element. In certain other examples, M′ can comprise at leasttwo different chemical elements and A′ can comprise at least onechemical element or M′ can comprise at least one chemical element and A′can comprise at least two different chemical elements. In certainexamples, M′ comprises one or more elements from Group IA (for example,lithium, sodium, rubidium, and cesium), Group IIA (for example,beryllium, magnesium, calcium, strontium, and barium), Group IIB (forexample, Zn, Cd, and Hg), Group IIIA (for example, B, Al, Ga, In, andTl), Group IVA (for example, Si, Ge, Sn, and Pb), or the transitionmetals (for example, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe,Co, Ni, Pd, Pt, Rh, and the like). (See, F. A. Cotton et al., AdvancedInorganic Chemistry, 6th Edition, (1999). In certain examples, A′comprises one or more elements selected from Group VA (for example,nitrogen, phosphorus, arsenic, antimony, and bismuth) and/or Group VIA(for example, oxygen, sulfur, selenium, and tellurium). Othersemiconductor materials suitable for inclusion in the shell, including,but not limited to, other examples disclosed in the detaileddescription, can be used. The second semiconductor material ispreferably an inorganic semiconductor material.

In certain embodiments, M′ comprises one or more chemical elements fromGroup IIA and/or Group IIB and A′ comprises one or more chemicalelements from Group VIA.

In certain embodiments, M′ comprises one or more chemical elements fromGroup IIA and/or Group IIB and A′ comprises one or more chemicalelements from Group VA.

In certain other embodiments, M′ comprises one or more chemical elementsfrom Group IIIA and A′ comprises one or more chemical elements fromGroup VA.

In certain embodiments, M′ comprises one or more chemical elements fromGroup IVA and A′ comprises one or more chemical elements from Group VIA.

In certain embodiments, M′ comprises one or more chemical elements fromGroup IA and/or Group IIIA and A′ comprises one or more chemicalelements from Group VIA.

In certain embodiments, M′ comprises one or more chemical elements fromGroup IIA and/or Group IVA and A′ comprises one or more chemicalelements from Group VA.

In certain embodiments, the second semiconductor material does notinclude an element from Group IIA.

In certain embodiments, the second semiconductor material is not anoxide.

In certain other embodiments, the second semiconductor materialcomprises zinc and sulfur. In certain embodiments, the secondsemiconductor material comprises ZnS.

In certain embodiments, the second semiconductor material can comprise amixture or alloy of the two or more semiconductor materials. In certainembodiments, two or more shells can be disposed over at least a portionof the core wherein each shell can include at least one semiconductormaterial and/or a mixture of two or more semiconductor materials. Eachshell may include one or more monolayers.

In certain embodiments, the shell can comprise an alloy of three or morechemical elements.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, the shell can comprise a homogeneous alloy ofthree or more chemical elements.

In certain embodiments, the first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1 and the second semiconductor materialcomprises ZnS.

In certain embodiments, the first semiconductor material can compriseZn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductor materialcan comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In accordance with another aspect of the invention there is provided asemiconductor nanocrystal including a core comprising a firstsemiconductor material comprising at least three chemical elements and ashell disposed over at least a portion of the core, the shell comprisinga second semiconductor material, wherein the semiconductor nanocrystalis capable of emitting blue light with a photoluminescence quantumefficiency greater than about 65% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 70% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 80% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 90% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 95% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency of about100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In certain embodiments, the blue light can include a maximum peakemission at a wavelength not greater than about 470 nm

In certain embodiments, the blue light can include a maximum peakemission at a wavelength not greater than about 480 nm

In certain embodiments, the blue light can include a maximum peakemission at a wavelength not greater than about 490 nm

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and sulfur.

In certain embodiments, a first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1. In certain embodiments, 0<x≦0.5. Incertain embodiments, 0<x≦0.3. In certain embodiments, 0.05<x<0.2. Incertain embodiments, 0.1≦x≦0.15. In certain embodiments, x is from about0.10 to about 0.12.

In certain embodiments wherein x≧0.1, a maximum peak emission can occurat a wavelength not greater than about 470 nm.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain other embodiments, the second semiconductor materialcomprises zinc and sulfur. In certain embodiments, the secondsemiconductor material comprises ZnS.

In certain embodiments, the second semiconductor material can comprise amixture or alloy of the two or more semiconductor materials. In certainembodiments, two or more shells can be disposed over at least a portionof the core wherein each shell can include at least one semiconductormaterial and/or a mixture of two or more semiconductor materials. Eachshell may include one or more monolayers.

In certain embodiments, the shell can comprise an alloy of three or morechemical elements.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, the shell can comprise a homogeneous alloy ofthree or more chemical elements.

In certain embodiments, the first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1 and the second semiconductor materialcomprises ZnS.

In certain embodiments, the first semiconductor material can compriseZn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductor materialcan comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In accordance with another aspect of the invention there is provided asemiconductor nanocrystal including a core comprising a firstsemiconductor material comprising at least three chemical elements and ashell disposed over at least a portion of the core, the shell comprisinga second semiconductor material comprising at least three chemicalelements, wherein the semiconductor nanocrystal is capable of emittinglight including a maximum peak emission in the blue region of thespectrum upon excitation.

In certain embodiments the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 490nm.

In certain embodiments the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 470nm.

In certain embodiments, the maximum peak emission has a full width athalf maximum of not more than 50 nm, not more than 40 nm, or not morethan 30 nm.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting light with a photoluminescence quantum efficiency of greaterthan about 60%.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain preferred embodiments, the first semiconductor material cancomprise Zn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductormaterial can comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, a shell comprising Cd_(x)Zn_(1−x)S wherein 0<x<1is obtainable by a process comprising adding Cd-precursor, Zn-precursor,and S-precursor to a nanocrystal core and subsequently adding additionalZn-precursor and S-precursor thereto.

In certain embodiments, the Cd-precursor, Zn-precursor, and S-precursorare admixed with nanocrystal cores at a temperature sufficient to induceformation of shell material on at least a portion of the surfaces of atleast a portion of the cores. The subsequently added additional amountsof Zn-precursor and S-precursor are admixed with the nanocrystal coresto which the Cd-precursor, Zn-precursor, and S-precursor has beenpreviously added. Preferably the temperature of the admixture to whichadditional Zn-precursor and S-precursor are added is at a temperaturesufficient to induce formation of additional shell material on at leasta portion of the surfaces of at least a portion of the cores includingshell material.

In accordance with another aspect of the invention, there is provided apopulation of semiconductor nanocrystals, wherein the population iscapable of emitting blue light including a maximum peak emission at awavelength not greater than about 470 nm with a photoluminescencequantum efficiency greater than about 65% upon excitation.

In certain embodiments the semiconductor nanocrystals can comprise afirst semiconductor material.

In certain embodiments, the semiconductor nanocrystals comprises acore/shell structure wherein the core comprises a first semiconductormaterial and a shell comprising a second semiconductor material whereinthe shell is disposed over at least a portion of a surface of the core.

Examples of semiconductor nanocrystals are described above and in thedetailed description.

In certain embodiments, the population is capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency greater than about70% upon excitation.

In certain embodiments, the population is capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency greater than about80% upon excitation.

In certain embodiments, the population is capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency greater than about90% upon excitation.

In certain embodiments, the population is capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency greater than about95% upon excitation.

In certain embodiments, the population is capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency of about 100% uponexcitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In accordance with another aspect of the invention, there is provided apopulation of semiconductor nanocrystals, wherein each nanocrystal ofthe population comprises a semiconductor nanocrystal including a corecomprising a first semiconductor material comprising at least threechemical elements and a shell disposed over at least a portion of thecore, the shell comprising a second semiconductor material, wherein thepopulation is capable of emitting blue light with a photoluminescencequantum efficiency greater than about 65% upon excitation.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

The population is capable of emitting blue light with aphotoluminescence quantum efficiency greater than about 65% uponexcitation.

In certain embodiments, the population is capable of emitting blue lightwith a photoluminescence quantum efficiency greater than about 70% uponexcitation.

In certain embodiments, the population is capable of emitting blue lightwith a photoluminescence quantum efficiency greater than about 80% uponexcitation.

In certain embodiments, the population is capable of emitting blue lightwith a photoluminescence quantum efficiency greater than about 90% uponexcitation.

In certain embodiments, the population is capable of emitting blue lightwith a photoluminescence quantum efficiency greater than about 95% uponexcitation.

In certain embodiments, the population is capable of emitting blue lightwith a photoluminescence quantum efficiency of about 100% uponexcitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 470 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 480 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 490 nm.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and sulfur.

In certain embodiments, a first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1. In certain embodiments, 0<x≦0.5. Incertain embodiments, 0<x≦0.3. In certain embodiments, 0.05<x<0.2. Incertain embodiments, 0.1≦x≦0.15. In certain embodiments, x is from about0.10 to about 0.12.

In certain embodiments wherein x≧0.1, a maximum peak emission can occurat a wavelength not greater than about 470 nm.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain other embodiments, the second semiconductor materialcomprises zinc and sulfur. In certain embodiments, the secondsemiconductor material comprises ZnS.

In certain embodiments, the second semiconductor material can comprise amixture or alloy of the two or more semiconductor materials. In certainembodiments, two or more shells can be disposed over at least a portionof the core wherein each shell can include at least one semiconductormaterial and/or a mixture of two or more semiconductor materials. Eachshell may include one or more monolayers.

In certain embodiments, the shell can comprise an alloy of three or morechemical elements.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, the shell can comprise a homogeneous alloy ofthree or more chemical elements.

In certain embodiments, the first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1 and the second semiconductor materialcomprises ZnS.

In certain embodiments, the first semiconductor material can compriseZn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductor materialcan comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In accordance with another aspect of the invention, there is provided apopulation of semiconductor nanocrystals, wherein each nanocrystal ofthe population comprises a core comprising a first semiconductormaterial comprising at least three chemical elements and a shelldisposed over at least a portion of the core, the shell comprising asecond semiconductor material comprising at least three chemicalelements. The population upon excitation is capable of emitting lightincluding a maximum peak emission in the blue region of the spectrum.

In certain embodiments the population, upon excitation, is capable ofemitting light including a maximum peak emission a wavelength notgreater than about 490 nm.

In certain embodiments the population, upon excitation, is capable ofemitting light including a maximum peak emission a wavelength notgreater than about 470 nm.

In certain embodiments, the maximum peak emission has a full width athalf maximum of not more than 50 nm, not more than 40 nm, or not morethan 30 nm.

In certain embodiments, the population is capable of emitting lightincluding a maximum peak emission in the blue region of the spectrumwith a photoluminescence quantum efficiency of greater than about 60%.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain preferred embodiments, the first semiconductor material cancomprise Zn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductormaterial can comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, a shell comprising Cd_(x)Zn_(1−x)S wherein 0<x<1is obtainable by a process comprising adding Cd-precursor, Zn-precursor,and S-precursor to a nanocrystal core and subsequently adding additionalZn-precursor and S-precursor thereto.

In certain embodiments of populations of semiconductor nanocrystals inaccordance with the invention, the semiconductor nanocrystals includedin the population is preferably of a substantially monodisperse, andmore preferably, of a monodisperse, size.

In certain embodiments of populations of semiconductor nanocrystals inaccordance with the invention, a semiconductor nanocrystal included inthe population further include one or more ligands attached to the outersurface thereof.

In still a further aspect of the present invention there is provided acomposition including a semiconductor nanocrystal capable of emittingblue light including a maximum peak emission at a wavelength not greaterthan about 470 nm with a photoluminescence quantum efficiency greaterthan about 65% upon excitation.

In certain embodiments the semiconductor nanocrystal can comprise afirst semiconductor material.

In certain embodiments, the semiconductor nanocrystal comprises acore/shell structure wherein the core comprises a first semiconductormaterial and a shell comprising a second semiconductor material whereinthe shell is disposed over at least a portion of a surface of the core.

Examples of semiconductor nanocrystals are described above and in thedetailed description.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 70% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 80% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 90% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 95% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isabout 100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In still a further aspect of the present invention there is provided acomposition including a semiconductor nanocrystal including a corecomprising a first semiconductor material comprising at least threechemical elements and a shell disposed over at least a portion of thecore, the shell comprising a second semiconductor material, wherein thesemiconductor nanocrystal is capable of emitting blue light with aphotoluminescence quantum efficiency greater than about 65% uponexcitation.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 70% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 80% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 90% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 95% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency of about100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 470 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 480 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 490 nm.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and sulfur.

In certain embodiments, a first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1. In certain embodiments, 0<x≦0.5. Incertain embodiments, 0<x≦0.3. In certain embodiments, 0.05<x<0.2. Incertain embodiments, 0.1≦x≦0.15. In certain embodiments, x is from about0.10 to about 0.12.

In certain embodiments wherein x≧0.1, a maximum peak emission can occurat a wavelength not greater than about 470 nm.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain other embodiments, the second semiconductor materialcomprises zinc and sulfur. In certain embodiments, the secondsemiconductor material comprises ZnS.

In certain embodiments, the second semiconductor material can comprise amixture or alloy of the two or more semiconductor materials. In certainembodiments, two or more shells can be disposed over at least a portionof the core wherein each shell can include at least one semiconductormaterial and/or a mixture of two or more semiconductor materials. Eachshell may include one or more monolayers.

In certain embodiments, the shell can comprise an alloy of three or morechemical elements.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, the shell can comprise a homogeneous alloy ofthree or more chemical elements.

In certain embodiments, the first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1 and the second semiconductor materialcomprises ZnS.

In certain embodiments, the first semiconductor material can compriseZn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductor materialcan comprise Cd_(x)Zn_(1−x)S wherein 0<x<1. In still a further aspect ofthe present invention there is provided a composition including asemiconductor nanocrystal, semiconductor nanocrystal including a corecomprising a first semiconductor material comprising at least threechemical elements and a shell disposed over at least a portion of thecore, the shell comprising a second semiconductor material comprising atleast three chemical elements, wherein the semiconductor nanocrystal iscapable of emitting light including a maximum peak emission in the blueregion of the spectrum upon excitation.

In certain embodiments the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 490nm.

In certain embodiments the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 470nm.

In certain embodiments, the maximum peak emission has a full width athalf maximum of not more than 50 nm, not more than 40 nm, or not morethan 30 nm.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting light with a photoluminescence quantum efficiency of greaterthan about 60%.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain preferred embodiments, the first semiconductor material cancomprise Zn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductormaterial can comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, a shell comprising Cd_(x)Zn_(1−x)S wherein 0<x<1is obtainable by a process comprising adding Cd-precursor, Zn-precursor,and S-precursor to a nanocrystal core and subsequently adding additionalZn-precursor and S-precursor thereto.

In certain embodiments of compositions in accordance with the presentinvention, a semiconductor nanocrystal included in the compositionfurther includes one or more ligands attached to the outer surfacethereof.

In certain embodiments of compositions in accordance with the presentinvention, a plurality of semiconductor nanocrystals are included in thecomposition.

In certain embodiments of compositions in accordance with the presentinvention, the plurality of semiconductor nanocrystals included in thecomposition are preferably of a substantially monodisperse, and morepreferably, of a monodisperse, size.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a polymer.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a pre-polymer.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes an oligomer.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a small molecule.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes an inorganic material.

In further embodiments of compositions in accordance with the presentinvention, the composition comprises a matrix. The matrix can comprisean organic or inorganic material.

In certain embodiments of compositions in accordance with the presentinvention, the semiconductor nanocrystals are dispersed in the matrix.In certain embodiments, the semiconductor nanocrystals are randomlydispersed in the matrix. In certain embodiments, the semiconductornanocrystals are homogeneously dispersed in the matrix.

Non-limiting examples of matrices include, but are not limited to, apolymer (e.g., polystyrene, epoxy, polyimides), a glass (e.g., silicaglass), a gel (e.g., a silica gel), and any other material which is atleast partially, and preferably fully, transparent to the light emittedby the semiconductor nanocrystals and in which semiconductornanocrystals can be included. Depending on the use of the composition,the matrix can be conductive or non-conductive. Examples of preferredmatrices include, but are not limited to, glass or a resin. Resins canbe non-curable resins, heat-curable resins, or photocurable resins. Morespecific examples of resins can be in the form of either an oligomer ora polymer, a melamine resin, a phenol resin, an alkyl resin, an epoxyresin, a polyurethane resin, a maleic resin, a polyamide resin,polymethyl methacrylate, polyacrylate, polycarbonate, polyvinyl alcohol,polyvinylpyrrolidone, hydroxyethylcellulose, carboxymethylcellulose,copolymers containing monomers forming these resins, and the like.Examples of a photo-polymerizable resin include an acrylic acid ormethacrylic acid based resin containing a reactive vinyl group, aphoto-crosslinkable resin which generally contains a photo-sensitizer,such as polyvinyl cinnamate, or the like. A heat-curable resin mayselected when the photo-sensitizer is not used. Matrix resins may beused individually or in combination of two or more. Other matrixmaterials can be readily identified by one of ordinary skill in the art.In certain embodiments, a composition including a matrix may furtherinclude scatterers (e.g., without limitation, metal or metal oxideparticles, air bubbles, and glass and polymeric beads (solid or hollow),and/or other optional additives typically used in the desired end-useapplication for the composition.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a liquid medium. In certainembodiments, compositions in accordance with the present inventionincluding a liquid medium comprise an ink. Examples of suitable liquidsand other optional additives that may be included in an ink aredescribed in International Application No. PCT/US2007/00873 of SethCoe-Sullivan et al., for “Composition Including Material, Methods OfDepositing Material, Articles Including Same And Systems For DepositionMaterial”, filed 9 Apr. 2007, and International Application No.PCT/US2007/014711 of Seth Coe-Sullivan et al., for “Methods ForDepositing Nanomaterial, Methods For Fabricating A device, And MethodsFor Fabricating An Array Of Devices”, filed 25 Jun. 2007, which are eachhereby incorporated herein by reference in their entireties.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a non-polar liquid in whichthe semiconductor nanocrystal is dispersible.

In certain embodiments of compositions in accordance with the presentinvention, the composition further includes a polar liquid in which thesemiconductor nanocrystal is dispersible.

In a still further aspect of the invention there is provided a deviceincluding a semiconductor nanocrystal capable of emitting blue lightincluding a maximum peak emission at a wavelength not greater than about470 nm with a photoluminescence quantum efficiency greater than about65% upon excitation.

In certain embodiments the semiconductor nanocrystal can comprise afirst semiconductor material.

In certain embodiments, the semiconductor nanocrystal comprises acore/shell structure wherein the core comprises a first semiconductormaterial and a shell comprising a second semiconductor material whereinthe shell is disposed over at least a portion of a surface of the core.

In certain embodiments, a device comprises a layer comprising aplurality of semiconductor nanocrystals and means for exciting thesemiconductor nanocrystals, wherein the plurality of semiconductornanocrystals include one or more semiconductor nanocrystals capable ofemitting blue light including a maximum peak emission at a wavelengthnot greater than about 470 nm with a photoluminescence quantumefficiency greater than about 65% upon excitation. The layer can becontinuous or non-continuous. The layer can be patterned or unpatterned.In certain embodiments the semiconductor nanocrystal can comprise afirst semiconductor material. In certain embodiments, the semiconductornanocrystal comprises a core/shell structure wherein the core comprisesa first semiconductor material and a shell comprising a secondsemiconductor material wherein the shell is disposed over at least aportion of a surface of the core. Examples of semiconductor nanocrystalsare described above and in the detailed description.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 70% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 80% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 90% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isgreater than about 95% upon excitation.

In certain embodiments, the photoluminescence quantum efficiency isabout 100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In a still further aspect of the invention there is provided a deviceincluding a semiconductor nanocrystal including a core comprising afirst semiconductor material comprising at least three chemical elementsand a shell disposed over at least a portion of the core, the shellcomprising a second semiconductor material, wherein the semiconductornanocrystal is capable of emitting blue light with a photoluminescencequantum efficiency greater than about 65% upon excitation.

In certain embodiments, a device comprises a layer comprising aplurality of semiconductor nanocrystals and means for exciting thesemiconductor nanocrystals, wherein the plurality of semiconductornanocrystals include one or more semiconductor nanocrystals including acore comprising a first semiconductor material comprising at least threechemical elements and a shell disposed over at least a portion of thecore, the shell comprising a second semiconductor material, wherein thesemiconductor nanocrystal is capable of emitting blue light with aphotoluminescence quantum efficiency greater than about 65% uponexcitation. The layer can be continuous or non-continuous. The layer canbe patterned or unpatterned.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 70% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 80% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 90% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency greaterthan about 95% upon excitation.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting blue light with a photoluminescence quantum efficiency of about100% upon excitation.

In certain embodiments, the blue light includes a maximum peak emissionwith a full width at half maximum of not more than 50 nm, not more than40 nm, not more than 30 nm, or not more than 20 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 470 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 480 nm.

In certain embodiments, the blue light can include an emission maximumpeak at a wavelength not greater than about 490 nm.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and sulfur.

In certain embodiments, a first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1. In certain embodiments, 0<x≦0.5. Incertain embodiments, 0<x≦0.3. In certain embodiments, 0.05<x<0.2. Incertain embodiments, 0.1≦x≦0.15. In certain embodiments, x is from about0.10 to about 0.12.

In certain embodiments wherein x≧0.1, a maximum peak emission can occurat a wavelength not greater than about 470 nm.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain other embodiments, the second semiconductor materialcomprises zinc and sulfur. In certain embodiments, the secondsemiconductor material comprises ZnS.

In certain embodiments, the second semiconductor material can comprise amixture or alloy of the two or more semiconductor materials. In certainembodiments, two or more shells can be disposed over at least a portionof the core wherein each shell can include at least one semiconductormaterial and/or a mixture of two or more semiconductor materials. Eachshell may include one or more monolayers.

In certain embodiments, the shell can comprise an alloy of three or morechemical elements.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, the shell can comprise a homogeneous alloy ofthree or more chemical elements.

In certain embodiments, the first semiconductor material comprisesZn_(x)Cd_(1−x)S, wherein 0<x<1 and the second semiconductor materialcomprises ZnS.

In certain embodiments, the first semiconductor material can compriseZn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductor materialcan comprise Cd_(x)Zn_(1−x)S wherein 0<x<1. In a still further aspect ofthe invention there is provided a device including a semiconductornanocrystal comprising a core comprising a first semiconductor materialcomprising at least three chemical elements and a shell disposed over atleast a portion of the core, the shell comprising a second semiconductormaterial comprising at least three chemical elements, wherein thesemiconductor nanocrystal is capable of emitting light including amaximum peak emission in the blue region of the spectrum uponexcitation.

In certain embodiments the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 490nm.

In certain embodiments, the emission in the blue region of the spectrumhas a maximum peak emission at a wavelength not greater than about 470nm.

In certain embodiments, the maximum peak emission has a full width athalf maximum of not more than 50 nm, not more than 40 nm, or not morethan 30 nm.

In certain embodiments, the semiconductor nanocrystal is capable ofemitting light with a photoluminescence quantum efficiency of greaterthan about 60%.

Examples of first semiconductor materials and second semiconductormaterials are described above and in the detailed description.

In certain embodiments, the first semiconductor material comprises zinc,cadmium, and selenium.

In certain embodiments, the first semiconductor material comprisesZn_(1−x)Cd_(x)Se, wherein 0<x<1.

In certain embodiments, the second semiconductor material compriseszinc, cadmium, and sulfur.

In certain embodiments, the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.

In certain preferred embodiments, the first semiconductor material cancomprise Zn_(1−x)Cd_(x)Se, wherein 0<x<1, and the second semiconductormaterial can comprise Cd_(x)Zn_(1−x)S wherein 0<x<1.

In certain embodiments, a shell comprising Cd_(x)Zn_(1−x)S wherein 0<x<1is obtainable by a process comprising adding Cd-precursor, Zn-precursor,and S-precursor to a nanocrystal core and subsequently adding additionalZn-precursor and S-precursor thereto.

In certain embodiments of devices in accordance with the presentinvention, the plurality of semiconductor nanocrystals are preferably ofa substantially monodisperse, and more preferably, of a monodisperse,size.

In certain embodiments, means for exciting the semiconductornanocrystals comprises a light source.

In certain embodiments of devices in accordance with the presentinvention, means for exciting the semiconductor nanocrystals comprises alight source. Suitable light sources are known or can be readilyascertained by one of ordinary skill in the art.

In certain embodiments of devices in accordance with the presentinvention, means for exciting the semiconductor nanocrystals comprises afirst electrode and a second electrode opposed to the first electrodeand the layer comprising semiconductor nanocrystals is disposed betweenthe two electrodes and in electrical communication therewith. In certainembodiments, one of the electrodes can be supported by a substrate(which can be flexible or rigid). In certain embodiments, the devicefurther includes at least one charge transport layer between the twoelectrodes. In certain embodiments, two charge transport layers areincluded, e.g., a hole transport layer and an electron transport layer.In certain embodiments, two charge transport layers, e.g., a holetransport layer and an electron transport layer, and a hole blockinglayer are included. In certain other embodiments, additional layers canbe included. Charge transport materials, hole blocking materials, andother materials that may be included in a device can be identified by aperson having ordinary skill in the art. In a device includingsemiconductor nanocrystals capable of emitting blue light, for example,a hole transport layer comprising 4-4′-N,N′-dicarbazolyl-biphenyl (CBP)and an electron transport layer comprising2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TBPi) canbe used. U.S. Provisional Patent Application No. 60/825,374, filed 12Sep. 2006, of Seth A. Coe-Sullivan et al., for “Light-Emitting DevicesAnd Displays With Improved Performance”. Additional informationconcerning devices, device structures, examples of materials for use invarious device structures, etc. is discussed in U.S. Provisional PatentApplication No. 60/825,374, filed 12 Sep. 2006, of Seth A. Coe-Sullivanet al., for “Light-Emitting Devices And Displays With ImprovedPerformance”, which is hereby incorporated herein by reference, andelsewhere herein. Examples of other device structures that can be usefulin making devices including semiconductor nanocrystals capable ofemitting light in the blue region of the spectrum upon electricalexcitation are described in U.S. Application No. 60/866,262, filed 23Jan. 2007, of Peter T. Kazlas, et al., for “Light-Emitting Devices AndDisplays With Improved Performance”, and International Application No.PCT/US2007/024310, filed on 21 Nov. 2007, of Peter T. Kazlas, et al.,for “Light Emitting Devices And Displays With Improved Performance”(International Publication No. WO 2008/063657), each of which is herebyincorporated herein by reference in its entirety. For additionalinformation concerning devices, light sources, and compositions seealso, for example, U.S. Pat. No. 5,434,878 of Lawandy; U.S. Pat. No.5,882,779 of Lawandy; U.S. Pat. No. 6,890,777 of Bawendi et al.; U.S.Pat. No. 6,803,719 of Miller et al. Each of the foregoing patents ishereby incorporated herein by reference in its entirety.

In certain embodiments, devices in accordance with the present inventioncomprise a light-emitting device. In certain other embodiments, devicesin accordance with the present invention comprise a display device. Incertain other embodiments, devices in accordance with the presentinvention comprise a solid state lighting device.

In certain embodiments of the inventions described or contemplated bythis general description, the following detailed description, andclaims, the photoluminescence quantum efficiency can be determined whenthe semiconductor nanocrystals are dispersed in anhydrous hexane andexcited by 373 nm light at room temperature. The concentration ofsemiconductor nanocrystals in the dispersion can be in a range betweenabout 0.1 to about 1 weight percent, e.g., about 10 mg/ml, etc.

In certain embodiments of the inventions described or contemplated bythis general description, the following detailed description, andclaims, the semiconductor nanocrystals are preferably of a substantiallymonodisperse, and more preferably, of a monodisperse, size.

In certain embodiments of the inventions described or contemplated bythis general description, the following detailed description, andclaims, a semiconductor nanocrystal can include one or more ligandsattached to the outer surface thereof.

In certain embodiments of the inventions described or contemplated bythis general description, the following detailed description, and claimsincluding a second semiconductor material, the second semiconductormaterial preferably has a composition that is different from thecomposition of the core. Although, in certain embodiments, a shell maycomprise a second semiconductor material with the same composition asthat of the first semiconductor material. In certain embodiments, thesecond semiconductor material can comprise a mixture or alloy of the twoor more semiconductor materials. In certain embodiments, two or moreshells can be disposed over at least a portion of the core wherein eachshell can include single semiconductor material and/or a mixture of oneor more semiconductor materials. Each shell may include one or moremonolayers.

Photoluminescence quantum efficiency (also referred to as quantum yieldor solution quantum yield) represents the percent of absorbed photonsthat are reemitted as photons.

The foregoing, and other aspects described herein all constituteembodiments of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Other embodimentswill be apparent to those skilled in the art from consideration of thedescription, from the claims, and from practice of the inventiondisclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor nanocrystal is capable of emitting light uponexcitation. A semiconductor nanocrystal can be excited by irradiationwith an excitation wavelength of light, by electrical excitation, or byother energy transfer.

A semiconductor nanocrystal is a nanometer sized particle, e.g., in thesize range of up to about 1000 nm. In certain embodiments, asemiconductor nanocrystal can have a size in the range of up to about100 nm. In certain embodiments, a semiconductor nanocrystal can have asize in the range up to about 20 nm (such as about 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm). In certainpreferred embodiments, a semiconductor nanocrystal can have a size lessthan 100 Å. In certain preferred embodiments, a semiconductornanocrystal has a size in a range from about 1 to about 6 nanometers andmore particularly from about 1 to about 5 nanometers. The size of asemiconductor nanocrystal can be determined, for example, by directtransmission electron microscope measurement. Other known techniques canalso be used to determine nanocrystal size.

A semiconductor nanocrystals can have various shapes. Examples of theshape of a nanocrystal include, but are not limited to, sphere, rod,disk, tetrapod, other shapes, and/or mixtures thereof.

In certain preferred embodiments, a semiconductor nanocrystal includes acore/shell structure.

Examples of preferred inorganic semiconductor materials that can beincluded in a semiconductor nanocrystal, a core and/or a shell includeinorganic semiconductor materials that can be represented by the generalformula MA. (This general formula does not represent the actual relativemolar amounts of the various chemical elements comprising the inorganicsemiconductor material.) In certain examples M comprises, for example,one or more elements from Group IA element (for example, lithium,sodium, rubidium, and cesium), Group IIA (for example, beryllium,magnesium, calcium, strontium, and barium), Group IIB (for example, Zn,Cd, and Hg), Group IIIA (for example, B, Al, Ga, In, and Ti), Group IVA(for example, Si, Ge, Sn, and Pb), and/or the transition metals (forexample, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Co, Ni, Pd,Pt, Rh, and the like). (See, F. A. Cotton et al., Advanced InorganicChemistry, 6th Edition, (1999). In certain examples, A comprises one ormore elements from Group VA (for example, nitrogen, phosphorus, arsenic,antimony, and bismuth) and/or Group VIA (for example, oxygen, sulfur,selenium, and tellurium). Examples of materials represented by theformula MA include Group II-VI compounds, Group II-V compounds, GroupIII-VI compounds, Group III-V compounds, Group IV-VI compounds, GroupI-III-VI compounds, Group II-IV-VI compounds, Group II-IV-V compounds,and/or mixtures or alloys thereof, including ternary and quaternarymixtures or alloys. Other inorganic semiconductor materials will bereadily ascertainable by one of ordinary skill in the art.

Alternatively, a semiconductor nanocrystal, a semiconductor nanocrystalcore and/or a shell can comprise, for example, a Group IV element. Incertain embodiments, a semiconductor nanocrystal is crystalline.

As discussed herein, in certain embodiments, three or more chemicalelements included in a semiconductor nanocrystal, a semiconductornanocrystal core and/or a shell can comprise an alloy. The alloy can behomogeneous or non-homogeneous. In certain embodiments including a firstsemiconductor and/or second semiconductor material, one or both of thefirst and second semiconductor materials can comprise an alloy, eitheror both of which can be homogeneous or non-homogeneous. A homogeneousalloyed semiconductor nanocrystal, core, and/or shell can be identifiedby techniques that are known to the person of ordinary skill in the art.See, for example, U.S. Pat. No. 7,056,0471 of Han et al., for “TernaryAnd Quaternary Nanocrystals, Processes For Their Production And UsesThereof”, issued 6 Jun. 2006.

Non-limiting examples of semiconductor materials that comprise three ormore chemical elements include those represented by the general formulaMA wherein M comprises at least two different chemical elements and Acomprises at least one chemical element or wherein M comprises at leastone chemical element and A comprises at least two different chemicalelements.

In certain embodiments of semiconductor nanocrystals including acore/shell structure, a core/shell nanocrystal can have an averagediameter from, for example, about 3 to about 55 nm, from about 3 toabout 40 nm, from about 3 to about 25 nm, from about 3 to about 10 nm,etc. In certain embodiments, the average diameter of a nanocrystal corecan be, for example, from about 1 to about 7 nm, from about 1 to about 4nm, from about 2 to about 3 nm, from about 4 to about 7 nm, etc. Anexample of an average thickness for a shell is from about 1 to about 3nm, which corresponds to an approximately 10 monolayer thickness. (Insuch example, a monolayer thickness would be approximately from about 1to about 3 Angstroms.)

The actual monolayer thickness is dependent upon the size andcomposition of the molecules included in the shell.

In certain embodiments of the invention, the core can comprise an alloyof the chemical elements.

In certain embodiments, the core can comprise a homogeneous alloy of thechemical elements.

In certain embodiments of the invention, the shell can comprise an alloyof the chemical elements.

In certain embodiments, the shell can comprise a homogeneous alloy ofthe chemical elements.

In certain embodiments, a semiconductor nanocrystal can include one ormore ligands attached to the outer surface thereof.

Selection of the composition of a semiconductor nanocrystal, as well asthe size of the semiconductor nanocrystal, can affect the characteristicspectral emission wavelength of the semiconductor nanocrystal. Thus, asone of ordinary skill in the art will realize, a particular compositionof a core will be selected based upon the spectral region desired. Ananocrystal core that emits energy in the visible range of the spectrumcan comprise, by way of non-limiting example, CdS, CdSe, CdTe, ZnSe,ZnTe, GaP, GaAs, etc. Semiconductor nanocrystal cores that emit energyin the near IR range include, but are not limited to, InP, InAs, InSb,PbS, PbSe, etc. Semiconductor nanocrystal cores that emit energy in theblue to near-ultraviolet include, but are not limited to ZnS, GaN, etc.For any particular composition selected for inclusion in a semiconductornanocrystal core contemplated, it is possible to tune the emission to adesired wavelength by controlling the thickness of the shell, based onthe band gap of the shell material.

For applications that utilize the luminescent properties of ananocrystal, the semiconductor nanocrystal size is selected such thatthe nanocrystal exhibits quantum confinement. Such applications include,but are not limited to, light-emitting devices, lasers, biomedical tags,photoelectric devices, solar cells, catalysts, and the like.Light-emitting devices including nanocrystals in accordance with thepresent invention may be incorporated into a wide variety of consumerproducts, including, but not limited to, flat panel displays, computermonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads up displays, fully transparentdisplays, flexible displays, laser printers, telephones, cell phones,personal digital assistants (PDAs), laptop computers, digital cameras,camcorders, viewfinders, micro-displays, vehicles, a large area wall,theater or stadium screen, or a sign. Various control mechanisms may beused to control such devices, including passive matrix and activematrix.

An example of a method of manufacturing a semiconductor nanocrystal or acore for a semiconductor nanocrystal including a core/shell structurecomprises a colloidal growth process. Colloidal growth occurs byinjection of the precursors for the semiconductor nanocrystal or core,as the case may be, in the case of a first semiconductor material, e.g.,an M donor and an A donor, into a hot coordinating or non-coordinatingsolvent. One example of a method for preparing monodispersesemiconductor nanocrystals comprises pyrolysis of organometallicreagents, such as dimethyl cadmium, injected into a hot, coordinatingsolvent. This permits discrete nucleation and results in the controlledgrowth of macroscopic quantities of semiconductor nanocrystal cores. Theinjection produces a nucleus that can be grown in a controlled manner toform a semiconductor nanocrystal or core. The reaction mixture can begently heated to grow and anneal the semiconductor nanocrystal or core.Both the average size and the size distribution of the semiconductornanocrystals or cores in a sample are dependent on the growthtemperature. The growth temperature necessary to maintain steady growthincreases with increasing average crystal size. The semiconductornanocrystal or core is a member of a population of semiconductornanocrystals. As a result of the discrete nucleation and controlledgrowth, the population of semiconductor nanocrystals or cores that canbe obtained has a narrow, monodisperse distribution of diameters. Themonodisperse distribution of diameters can also be referred to as asize. Preferably, a monodisperse population of nanocrystals includes apopulation of particles wherein at least about 60% of the particles inthe population fall within a specified particle size range. A populationof monodisperse particles preferably deviate less than 15% rms(root-mean-square) in diameter, more preferably less than 10% rms andmost preferably less than 5%.

In certain embodiments, the preparation of semiconductor nanocrystal orcores can be carried out in the presence of an amine. See, for example,U.S. Pat. No. 6,576,291 for “Preparation of Nanocrystallites” of Bawendiet al. issued 10 Jun. 2003, which is hereby incorporated herein byreference in its entirety.

The narrow size distribution of the semiconductor nanocrystals (e.g.,semiconductor nanocrystals including or not including a core/shellstructure, cores, etc.) allows the possibility of light emission innarrow spectral widths. Monodisperse semiconductor nanocrystals havebeen described in detail in Murray et al. (J. Am. Chem. Soc., 115:8706(1993)); in thesis of Christopher Murray, “Synthesis andCharacterization of II-VI Quantum Dots and Their Assembly into 3-DQuantum Dot Superlattices”, Massachusetts Institute of Technology,September, 1995; and in U.S. patent application Ser. No. 08/969,302 for“Highly Luminescent Color-Selective Materials”. The foregoing is herebyincorporated herein by reference in their entireties.

The process of controlled growth and annealing of the semiconductornanocrystals or cores in the coordinating solvent that followsnucleation can also result in uniform surface derivatization and regularstructures. As the size distribution sharpens, the temperature can beraised to maintain steady growth. By adding more M donor or A donor, thegrowth period can be shortened. In certain embodiments, an M donor cancomprise, for example, an inorganic compound, an organometalliccompound, or elemental metal. In certain embodiments, for example, M cancomprise cadmium, zinc, magnesium, mercury, aluminum, gallium, indium,thallium, etc. In certain embodiments, an A donor can comprise acompound capable of reacting with the M donor to form a material withthe general formula MA. For example, the A donor can comprise achalcogenide donor or a pnictide donor, such as elemental form dispersedin a solvent (e.g., Se in octadecene, S in an amine, etc.), a phosphinechalcogenide, a bis(silyl) chalcogenide, dioxygen, an ammonium salt, ora tris(silyl) pnictide. Additional examples of suitable A donorsinclude, but are not limited to, dioxygen, bis(trimethylsilyl) selenide((TMS)₂Se), trialkyl phosphine selenides such as (tri-noctylphosphine)selenide (TOPSe) or (tri-n-butylphosphine) selenide (TBPSe), trialkylphosphine tellurides such as (tri-n-octylphosphine) telluride (TOPTe) orhexapropylphosphorustriamide telluride (HPPTTe),bis(trimethylsilyl)telluride ((TMS)₂Te), bis(trimethylsilyl)sulfide((TMS)₂S), a trialkyl phosphine sulfide such as (tri-noctylphosphine)sulfide (TOPS), an ammonium salt such as an ammonium halide (e.g.,NH4Cl), tris(trimethylsilyl) phosphide ((TMS)₃P), tris(trimethylsilyl)arsenide ((TMS)₃As), or tris(trimethylsilyl) antimonide ((TMS)₃Sb). Incertain embodiments, the M donor and the A donor can be moieties withinthe same molecule.

Suitable solvents for use in preparing semiconductor nanocrystals,semiconductor nanocrystal cores, and/or shells include coordinatingsolvents and non-coordinating solvents. A coordinating solvent can helpcontrol the growth of the semiconductor nanocrystal core. A coordinatingsolvent is a compound having at least one donor site (e.g., loneelectron pair) that, for example, is available to coordinate to asurface of the growing semiconductor nanocrystal. Solvent coordinationcan stabilize the growing semiconductor nanocrystal. Examples ofcoordinating solvents include alkyl phosphines, alkyl phosphine oxides,alkyl phosphonic acids, or alkyl phosphinic acids, however, othercoordinating solvents, such as pyridines, furans, and amines may also besuitable for the semiconductor nanocrystal production. In certainembodiments, a coordinating solvent comprises pyridine, tri-n-octylphosphine (TOP), tri-n-octyl phosphine oxide (TOPO) andtrishydroxylpropylphosphine (tHPP), amines (including, but not limitedto, for example, decylamine, hexadecylamine, octadecylamine). Otherexamples include, octadecene, and squalene. Technical grade TOPO canalso be used.

Alternatively, a non-coordinating solvent can be used. Examples ofsuitable non-coordinating solvents include, but are not limited to,squalane, octadecane, and other saturated hydrocarbon solvents.

Other methods and method variations (e.g., including different solvents,precursors, reaction conditions, etc.) can also be used in preparingsemiconductor nanocrystals. Such methods and variations are within theskill of one of ordinary skill in the art.

Size distribution during the growth stage of the reaction can beestimated by monitoring the absorption and/or emission line widths ofthe particles. Modification of the reaction temperature in response tochanges in the absorption spectrum of the particles allows themaintenance of a sharp particle size distribution during growth.Reactants can be added to the nucleation solution during crystal growthto grow larger crystals as well as to sharpen size distribution. Forexample, for ZnS, CdSe, CdTe, PbSe, and InSb, by stopping growth at aparticular semiconductor nanocrystal average diameter and choosing theproper composition of the semiconducting material, the emission spectraof the semiconductor nanocrystals can be tuned continuously over thewavelength range of 300 nm to 5 microns, or from 400 nm to 800 nm. Bystopping growth at a particular semiconductor nanocrystal averagediameter, a population having an average semiconductor nanocrystaldiameter of less than 150 Å can be obtained. A population ofnanocrystals can have an average diameter of 15 Å to 125 Å.

The particle size distribution of the semiconductor nanocrystals can befurther refined by size selective precipitation with a poor solvent forthe semiconductor nanocrystals, such as methanol/butanol as described inU.S. Pat. No. 6,322,901. For example, semiconductor nanocrystals can bedispersed in a solution of 10% butanol in hexane. Methanol can be addeddropwise to this stirring solution until opalescence persists.Separation of supernatant and flocculate by centrifugation produces aprecipitate enriched with the largest nanocrystals in the sample. Thisprocedure can be repeated until no further sharpening of the opticalabsorption spectrum is noted. Size-selective precipitation can becarried out in a variety of solvent/nonsolvent pairs, includingpyridine/hexane and chloroform/methanol. The size-selected semiconductornanocrystal population preferably has no more than a 15% rms deviationfrom mean diameter, more preferably 10% rms deviation or less, and mostpreferably 5% rms deviation or less.

Transmission electron microscopy (TEM) can provide information about thesize, shape, and distribution of the semiconductor nanocrystalpopulation. Powder X-ray diffraction (XRD) patterns can provide the mostcomplete information regarding the type and quality of the crystalstructure of the semiconductor nanocrystals. Estimates of size are alsopossible since particle diameter is inversely related, via the X-raycoherence length, to the peak width. For example, the diameter of thesemiconductor nanocrystal can be measured directly by transmissionelectron microscopy or estimated from X-ray diffraction data using, forexample, the Scherrer equation. It also can be estimated from the UV/Visabsorption spectrum.

An example of a process for forming a shell over at least a portion of acore is described, for example, in U.S. Pat. No. 6,322,901, incorporatedherein by reference in its entirety. By adjusting the temperature of thereaction mixture during overcoating and monitoring the absorptionspectrum of the core, over coated materials having high emission quantumefficiencies and narrow size distributions can be obtained.Alternatively, a shell can be formed by exposing a core nanocrystalhaving a first composition and first average diameter to a population ofnanocrystals having a second composition and a second average diametersmaller than the first average diameter.

Examples of semiconductor materials that can be included in a shell arediscussed elsewhere herein.

In certain preferred embodiments, the shell comprises Cd_(x)Zn_(1−x)S,wherein 0<x<1. In preferred embodiments, a shell comprisingCd_(x)Zn_(1−x)S, wherein 0<x<1, is obtainable by a process comprisingadding Cd-precursor, Zn-precursor, and S-precursor to a nanocrystal coreand subsequently adding additional Zn-precursor and S-precursor thereto.

In certain embodiments, the Cd-precursor, Zn-precursor, and S-precursorare admixed with nanocrystal cores at a temperature sufficient to induceformation of shell material on at least a portion of the surfaces of atleast a portion of the cores. The subsequently added additional amountsof Zn-precursor and S-precursor are admixed with the nanocrystal coresto which the Cd-precursor, Zn-precursor, and S-precursor has beenpreviously added. Preferably the temperature of the admixture to whichadditional Zn-precursor and S-precursor are added is at a temperaturesufficient to induce formation of additional shell material on at leasta portion of the surfaces of at least a portion of the cores includingshell material.

Overcoating is preferably carried out in a liquid medium. In certainembodiments, the liquid medium comprises a coordinating solvent.Suitable coordinating solvents include any coordinating solvent that canbe used in preparation of nanocrystal cores. In certain embodiments, thesemiconductor nanocrystal cores are dispersed in the coordinatingsolvent. In certain other embodiments, the nanocrystal cores arecolloidally dispersed in the coordinating solvent during at least partof the overcoating process. In certain other embodiments, the liquidmedium can comprise a non-coordinating solvent.

In embodiments wherein a semiconductor nanocrystal comprises acore/shell structure, shell thickness can be varied by growing a desiredthickness of the shell. For example, the shell can have a thickness lessthan about one monolayer, about one monolayer, or more than about onemonolayer. The thickness is selected to achieve the predeterminedcharacteristics of the core/shell nanocrystal. For example, in certainembodiments, the shell thickness can be at least about one monolayer.Preferably, the thickness is less than that at which quantum confinementis not achieved. In certain embodiments, the thickness is in a rangefrom greater than 0 to about 20 monolayers. In certain embodiments, thethickness is in a range from greater than 0 to about 10 monolayers. Incertain embodiments, the thickness is in a range from greater than 0 toabout 5 monolayers. In certain embodiments, the thickness is in a rangefrom about 1 to about 5 monolayers. In certain embodiments, thethickness is in a range from about 3 to about 5 monolayers. In certainembodiments, more than 20 monolayers can be grown.

As discussed above, in certain embodiments, more than one shell can beincluded over a core.

By selecting and adjusting the temperature of the reaction mixtureduring overcoating and monitoring the absorption spectrum of the core,overcoated materials having high emission quantum efficiencies andnarrow size distributions can be obtained. The selection and adjustmentis within the skill of one of ordinary skill in the art.

In certain embodiments, the band gap of the shell material is greaterthan that of the core. In certain other embodiments, the band gap of theshell material is less than that of the core.

In certain embodiments, the shell is disposed on, for example, at least60%, at least 70%, at least 80%, at least 90% of the nanocrystal core.In certain preferred embodiment, the nanocrystal core is substantiallycompletely (e.g., greater than 95%, greater than 96%, greater than 97%,greater than 98%, greater than 99%) overcoated with the shell.

Precursors for a shell or second semiconductor material included in theshell can be in any form that is suitable for the generation of theshell. Such forms are known to or can be determined by the skilledperson. Examples of the numerous suitable precursors for M′ comprisingcadmium and zinc include organometallic compounds, for example,alkylated compounds such an dimethylzinc (ZnMe₂), diethylzinc (ZnEt₂),dimethylcadmium (CdMe₂), or as salts or long chain alkyl carboxylic acidderivatives such as cadmium stearate. Examples of suitable precursorsfor A′ comprising sulfur include bis(trimethylsilyl)sulfide ((TMS)₂S)(also referred to as hexamethyldisilathiane), elemental sulfur, etc.Precursors can be synthesized and used as stock solutions or made insitu. Examples of suitable precursor molecules of Cd, Zn, and S and thepreparation thereof, are described in Murray et al., supra; Cao andBanin, J. Am. Chem. Soc. 122, pages 9692 9702, (2000); Peng et al,supra, Dabboussi et al, J. Phys. Chem. B, 101, pages 9643 9475, (1997),or U.S. Pat. No. 6,322,901 for instance, the contents of all of whichare hereby incorporated by reference.

In certain embodiments of forming a shell over a core, semiconductornanocrystal cores, a liquid medium, and any optional additives areheated to a temperature between 100-360° C. prior to the addition of anyshell precursors. Preferably the mixture is heated to a temperature of170° C. In one embodiment the mixture is kept at a temperature ofapproximately 170° C. for between 5 minutes and 2 hours after additionof the precursors, preferably the mixture is kept at a temperature of170° C. for 10 minutes after addition of the precursors.

In certain embodiments, the precursors are preferably added inpredetermined amounts at a predetermined rate of addition.

Such additions can be carried out with use of a programmable meteringdevice. For small scale preparations, a programmable syringe pump can beused.

In certain embodiments, the precursors can be added as a continuousflow. In certain embodiments, for example, one or more of the precursorscan be added in a continuous liquid flow. In certain other embodiments,for example, all of the precursors can be added in a continuous liquidflow.

Alternatively, a continuous flow can be achieved in a gas flow.

In certain embodiments, the precursors can be added as a continuous flowat a predetermined rate.

A wealth of suitable high boiling point liquids exist that can be usedas coordinating solvents in the preparation of a shell. Among thedifferent types of high boiling point liquids that can be used are alkylphosphine/phosphine oxide/phosphite/phosphate/amine/phosphonicacid/ether/alkane, etc.

Specific examples of suitable liquids and liquid mixtures that aresuitable for use as coordinating solvents include but are not limited totrioctylphosphine, tributylphosphine, tri(dodecyl)phosphine,trioctylphosphine oxide, dibutyl-phosphite, tributyl phosphite,trioctadecyl phosphite, trilauryl phosphite, tris(tridecyl) phosphite,triisodecyl phosphite, bis(2-ethylhexyl)phosphate, tris(tridecyl)phosphate, hexadecylamine, oleylamine, octadecylamine,bis(2-ethylhexyl)amine, octylamine, dioctylamine, trioctylamine,dodecylamine/laurylamine, didodecylamine tridodecylamine,hexadecylamine, dioctadecylamine, trioctadecylamine, phenylphosphonicacid, hexylphosphonic acid, tetradecylphosphonic acid, octylphosphonicacid, octadecylphosphonic acid, propylenediphosphonic acid,phenylphosphonic acid, aminohexylphosphonic acid, dioctyl ether,diphenyl ether, methyl myristate, octyl octanoate, and hexyl octanoate.Other examples include squalene, and octadecene.

Examples of suitable non-coordinating solvents include, but are notlimited to, squalane, octadecane, and other saturated hydrocarbonsolvents.

Optionally, an amine can be further admixed with the nanocrystal coresand liquid medium prior to addition of the shell pre-cursors.

Examples of amines include, but are not limited to, primary alkyl amineor a primary alkenyl amine, such as a C₂-C₂₀ alkyl amine, a C₂-C₂₀alkenyl amine, preferably a C₈-C₁₈ alkyl amine or a C₈-C₁₈ alkenylamine. A preferred amine is decylamine.

The presence of amine in the liquid medium, whether in preparingsemiconductor nanocrystal, a semiconductor nanocrystal core and/or ashell, can contribute to the quality of the semiconductor nanocrystalobtained from an M or M′ donor (e.g., an M or M′-containing salt) and Aor A′ donor. In certain embodiments, the solvent comprises alkylphosphine oxide and includes an amine, wherein the amine and an alkylphosphine oxide are present in a mole ratio of, for example 10:90,30:70, or 50:50. A combined amine and solvent mixture can decrease sizedispersion and can improve photoluminescence quantum yield of thesemiconductor nanocrystal. For example, suitable amines for combiningwith tri-octylphosphine oxide (TOPO) include 1-hexadecylamine, oroleylamine. When the 1,2-diol or aldehyde and the amine are used incombination with the M-containing salt to form a population ofsemiconductor nanocrystals, the photoluminescence quantum efficiency andthe distribution of semiconductor nanocrystal sizes can be improved incomparison to semiconductor nanocrystals manufactured without the1,2-diol or aldehyde or the amine.

It is understood that the invention contemplates a semiconductornanocrystal including all sizes and shapes of semiconductornanocrystals, semiconductor nanocrystal cores, and/or core/shellstructures.

In certain preferred embodiments, a semiconductor nanocrystal inaccordance with the present invention can include at least one ligandattached thereto.

Preferably, a ligand comprises an organic material. A ligand may be anynumber of materials, but has an affinity for the semiconductornanocrystal surface. For example, a ligand can be an isolated organicmolecule, a polymer (or a monomer for a polymerization reaction), aninorganic complex, and an extended crystalline structure. A ligand canbe used to enhance the functionality, binding properties, dispersibilityof a coated semiconductor nanocrystal homogeneously into a chosenmedium, or the like. In addition, a ligand can be used to tailor theoptical properties of the semiconductor nanocrystal.

In certain embodiments, the ligands can be derived from the solvent usedduring the growth process. The surface can be modified by repeatedexposure to an excess of a competing coordinating group to form anoverlayer. For example, a dispersion of the capped semiconductornanocrystal can be treated with a coordinating organic compound, such aspyridine, to produce nanocrystals which disperse readily in pyridine,methanol, and aromatics but no longer disperse in aliphatic solvents.Such a surface exchange process can be carried out with any compoundcapable of coordinating to or bonding with the outer surface of thesemiconductor nanocrystal, including, for example, phosphines, thiols,amines and phosphates. The semiconductor nanocrystal can be exposed toshort chain polymers which exhibit an affinity for the surface and whichterminate in a moiety having an affinity for a liquid medium in whichthe semiconductor nanocrystal is suspended or dispersed. Such affinityimproves the stability of the suspension and discourages flocculation ofthe semiconductor nanocrystal.

The organic ligands can be useful in facilitating large area,non-epitaxial deposition of highly stable inorganic nanocrystals withina device.

More specifically, the coordinating ligand can have the formula:(Y—)_(k−n)—(X)-(-L)_(n)

wherein k is 2, 3 4, or 5, and n is 1, 2, 3, 4 or 5 such that k−n is notless than zero; X is O, O—S, O—Se, O—N, O—P, O—As, S, S═O, SO₂, Se,Se═O, N, N═O, P, P═O, C═O As, or As═O; each of Y and L, independently,is H, OH, aryl, heteroaryl, or a straight or branched C2-18 hydrocarbonchain optionally containing at least one double bond, at least onetriple bond, or at least one double bond and one triple bond. Thehydrocarbon chain can be optionally substituted with one or more C1-4alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, hydroxyl, halo, amino,nitro, cyano, C3-5 cycloalkyl, 3-5 membered heterocycloalkyl, aryl,heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4alkylcarbonyl, or formyl. The hydrocarbon chain can also be optionallyinterrupted by —O—, —S—, —N(R_(a))—, —N(R_(a))—C(O)—O—,—O—C(O)—N(R_(a))—, —N(R_(a))—C(O)—N(R_(b))—, —O—C(O)—O—, —P(R_(a))—, or—P(O)(R_(a))—. Each of R_(a) and R_(b), independently, is hydrogen,alkyl, alkenyl, alkynyl, alkoxy, hydroxylalkyl, hydroxyl, or haloalkyl.An aryl group is a substituted or unsubstituted aromatic group. Examplesinclude phenyl, benzyl, naphthyl, tolyl, anthracyl, nitrophenyl, orhalophenyl. A heteroaryl group is an aryl group with one or moreheteroatoms in the ring, for instance furyl, pyridyl, pyrrolyl,phenanthryl.

Monodentate alkyl phosphines (and phosphine oxides, the term phosphinein the following discussion of ligands will refer to both) can passivatenanocrystals efficiently. When nanocrystals with conventionalmonodentate ligands are diluted or embedded in a non-passivatingenvironment (i.e. one where no excess ligands are present), they canlose their high luminescence and their initial chemical inertness.Typical are an abrupt decay of luminescence, aggregation, and/or phaseseparation. In order to overcome these possible limitations, polydentateligands can be used, such as a family of polydentate oligomerizedphosphine ligands. The polydentate ligands show a high affinity betweenligand and nanocrystal surface. In other words, they are strongerligands, as is expected from the chelate effect of their polydentatecharacteristics.

Oligomeric phosphines have more than one binding site to the nanocrystalsurface, which ensures their high affinity to the nanocrystal surface.See, for example, for example, U.S. Ser. No. 10/641,292, filed Aug. 15,2003, (now U.S. Pat. No. 7,160,613), and U.S. Ser. No. 60/403,367, filedAug. 15, 2002, each of which is incorporated by reference in itsentirety. The oligomeric phosphine can be formed from a monomeric,polyfunctional phosphine, such as, for example,trishydroxypropylphosphine, and a polyfunctional oligomerizationreagent, such as, for example, a diisocyanate. The oligomeric phosphinecan be contacted with an isocyanate of formula R′-L-NCO, wherein L isC₂-C₂₄ alkylene, and

R′ has the formula

R′ has the formula

wherein R^(a) is hydrogen or C₁-C₄ alkyl, or R′ is hydrogen.

A suitable coordinating ligand can be purchased commercially or preparedby ordinary synthetic organic techniques, for example, as described inJ. March, Advanced Organic Chemistry, which is hereby incorporated byreference in its entirety.

Other ligands are described in U.S. patent application Ser. No.10/641,292 for “Stabilized Semiconductor Nanocrystals”, filed 15 Aug.2003, which is hereby incorporated herein by reference in its entirety.

EXAMPLES

The examples provided herein are provided as examples and notlimitations, wherein a number of modifications of the exemplifiedcompositions and processes are contemplated and within the scope of thepresent invention.

Unless otherwise specified, the following core preparations andmanipulations and shell preparations and manipulations were carried outin a nitrogen atmosphere.

Example 1A Core Preparation

0.026 g CdO (99.998% purity—Alfa) and 0.043 g of ZnO (99.999%purity—Sigma Aldrich) were weighed into a three necked flask equippedwith a condenser. To this was added: 2 ml tech grade oleic acid(Aldrich) and 16 ml of tech grade octadecene (ODE) (Aldrich). Thecontents of the flask were degassed at 80° C. for 20 minutes in vacuo(200 millitorr).

Separately 0.038 g of sulfur (99.999% Strem) was dissolved in 10 ml oftech grade ODE in a septum capped vial by stirring and heating in an oilbath to 130° C. While the sample was heating up, the pressure of thevessel was reduced to 200 millitorr until the oil bath temperature was85° C., then further heating was continued under nitrogen. After 1 hour,when all the sulfur was dissolved, the sample was cooled to roomtemperature.

The contents of the three necked flask were stirred and heated to 310°C. under nitrogen until all the oxides dissolved to give a clearsolution. The temperature controller was then set to 300° C. and oncethe temperature stabilized at 300° C., approximately 4.4 ml of S in ODEwas rapidly injected. The temperature of the solution fell to about 270°C. and climbed back to 300° C. in ˜30 minutes. The reaction was stoppedafter 3 hours and the contents of the flask were transferred to adegassed vial under nitrogen and transferred to an inert atmosphere boxfor further purification.

The cores were purified by precipitation as follows. (In this example,the precipitation step was carried out two times for each sample.) Thesolution was divided in half; each half was added to a separatecentrifuge tube. Excess butanol (˜20-30 ml) was added to each centrifugetube. Each tube was then centrifuged for 5 min, 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. After mixing, each centrifuge tube was centrifugedagain. The supernatant liquid from each centrifuge tube was transferredto a separate clean tube; the solids in each centrifuge tube werediscarded. Cores were precipitated from the supernatant liquid in eachof the separate tubes by adding excess butanol (20-25 ml) with stirring.The new tubes containing the precipitated cores were centrifuged, thesupernatant liquid decanted, leaving precipitated cores in each tube.˜5-6 ml anhydrous hexane were added to the precipitated cores in eachtube to solvate the cores and the contents of each tube was filteredthrough a 0.2 micron filter. (The cores are in the filtrate.)

A 2.5 μl aliquot of the filtrate was diluted 100 fold with anhydroushexane and a UV VIS spectrum of the diluted aliquot was measured andabsorbance at 350 nm measured.

Characterization of the Cores:—first peak 437 nm, abs=0.057, at 350 nm,abs=0.344

maximum peak emission—445 nm

FWHM=15 nm

Photoluminescence quantum efficiency ˜31%

Example 1B Shell Preparation (ZnS)

5 ml of 97% trioctylphosphine and 5 ml of oleylamine (distilled prior touse), were placed in a 4 necked flask equipped with a condenser andthermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N₂ to the flask and reducing the temperature to80° C., 4.2 ml of hexane containing core (see Example 1A above) wasadded and the solvent removed under vacuo for 2 hours. The temperaturewas raised to 170° C. and bis-trimethylsilylsulfide (137 mg) in 4 ml ofTOP and diethylzinc (47.4 mg) in 4 ml of TOP were added from separatesyringes at a rate of 50 microliters/minute. The solution in the flaskwas observed to develop a bluish color. After addition was complete, thesolution looked cloudy. The sample was transferred via a degassed vialinto an inert atmosphere box.

The cores including a ZnS shell were purified by precipitation asfollows. (In this example, the precipitation step was carried out twotimes for each sample.) were purified as follows. The solution wasdivided into 2 centrifuge tubes. Excess butanol (˜20-30 ml) was added toeach centrifuge tube. The centrifuge tubes were centrifuged for 5minutes at 4000 rpm. After centrifuging, the supernatant liquid waspoured off, retaining the solid in each centrifuge tube. ˜5 ml of hexanewas added to the solid in each centrifuge tube and the contents of eachcentrifuge tube were mixed using a vortexer. Semiconductor nanocrystalscomprising a core and a ZnS shell disposed over the core wereprecipitated by adding excess butanol (20-25 ml) with stirring. Thecentrifuge tube contents were centrifuged. The supernatant liquid wasdecanted, leaving the semiconductor nanocrystals in the centrifugetubes. ˜5 ml anhydrous hexane were added to the semiconductornanocrystals in one of the centrifuge tubes to solvate the semiconductornanocrystals. The hexane including the solvated semiconductornanocrystals was then transferred into the second centrifuge tube tosolvate the semiconductor nanocrystals contained therein. The mixtureincluding the hexane and the semiconductor nanocrystals from bothcentrifuge tubes was filtered through a 0.2 micron filter. (Theovercoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

maximum peak emission—446 nm

FWHM 17 nm

Photoluminescence quantum efficiency ˜100%

Example 2A Core Preparation

0.025 g CdO (99.998% Alfa) and 0.035 g of ZnO (99.999% Sigma Aldrich)were weighed into a three necked flask equipped with a condenser. Tothis was added: 2 ml tech grade oleic acid (Aldrich) and 16 ml of techgrade octadecene (ODE) (Aldrich). The contents of the flask weredegassed at 80° C. for 20 minutes in vacuo (200 millitorr).

Separately 0.035 g of sulfur (99.999% Strem) was dissolved in 10 ml oftech grade ODE in a septum capped vial by stirring and heating in an oilbath to 130° C. While the sample was heating up, the pressure of thevessel was reduced to 200 millitorr until the oil bath temperature was85° C., then further heating was continued under nitrogen. After 1 hour,when all the sulfur was dissolved, the sample was cooled to roomtemperature.

The contents of the three necked flask were stirred and heated to 310°C. under nitrogen until all the oxides dissolved to give a clearsolution. The temperature controller was then set to 300° C. and oncethe temperature stabilized at 300° C., approximately 4.0 ml of S in ODEwas rapidly injected. The temperature of the solution fell to about 270°C. and climbed back to 300° C. in ˜30 minutes. The reaction was stoppedafter 4 hours and the contents of the flask were transferred to adegassed vial under nitrogen and transferred to an inert atmosphere boxfor further purification.

The cores were purified by precipitation as follows. (In this example,the precipitation step was carried out two times for each sample.) Thesolution was divided in half; each half was added to a separatecentrifuge tube. Excess butanol (−20-30 ml) was added to each centrifugetube. Each tube was then centrifuged for 5 min, 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. After mixing, each centrifuge tube was centrifugedagain. The supernatant liquid from each centrifuge tube was transferredto a separate clean tube; the solids in each centrifuge tube werediscarded. Cores were precipitated from the supernatant liquid in eachof the separate tubes by adding excess butanol (20-25 ml) with stirring.The new tubes containing the precipitated cores were centrifuged, thesupernatant liquid decanted, leaving precipitated cores in each tube.˜5-6 ml anhydrous hexane were added to the precipitated cores in eachtube to solvate the cores and the contents of each tube was filteredthrough a 0.2 micron filter. (The cores are in the filtrate.)

A 2.5 μl aliquot of the filtrate was diluted 100 fold with anhydroushexane and a UV VIS spectrum of the diluted aliquot was measured andabsorbance at 350 nm measured.

Characterization of the Cores:—first peak 457 nm, abs=0.081, at 350 nm,abs=0.469

maximum peak emission—461 nm

FWHM 15 nm

Photoluminescence quantum efficiency ˜22%

Example 2B Shell Preparation (ZnS)

5 ml of 97% trioctylphosphine and 5 ml of oleylamine (distilled prior touse), were placed in a 4 necked flask equipped with a condenser andthermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N₂ to the flask and reducing the temperature to80° C., 3.5 ml of hexane containing cores (see Example 1A above) wasadded and the solvent removed under vacuo for 2 hours. The temperaturewas raised to 170° C. and bis-trimethylsilylsulfide (79.6 mg) in 4 ml ofTOP and diethylzinc (27.6 mg) in 4 ml of TOP were added from separatesyringes at a rate of 50 microliters/minute. The solution in the flaskwas observed to develop a bluish color. After addition was complete, thesolution looked cloudy. The sample was transferred via a degassed vialinto an inert atmosphere box.

The cores including a ZnS shell were purified by precipitation asfollows. (In this example, the precipitation step was carried out twotimes for each sample.) The solution was divided into 2 centrifugetubes. Excess butanol (˜20-30 ml) was added to each centrifuge tube. Thecentrifuge tubes were centrifuged for 5 minutes at 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. Semiconductor nanocrystals comprising a core and a ZnSshell disposed over the core were precipitated by adding excess butanol(20-25 ml) with stirring. The centrifuge tube contents were centrifuged.The supernatant liquid was decanted, leaving the semiconductornanocrystals in the centrifuge tubes. ˜5 ml anhydrous hexane were addedto the semiconductor nanocrystals in one of the centrifuge tubes tosolvate the semiconductor nanocrystals. The hexane including thesolvated semiconductor nanocrystals was then transferred into the secondcentrifuge tube to solvate the semiconductor nanocrystals containedtherein. The mixture including the hexane and the semiconductornanocrystals from both centrifuge tubes was filtered through a 0.2micron filter. (The overcoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

maximum peak emission—464 nm

FWHM 17 nm

Photoluminescence quantum efficiency ˜74%

Example 3A Core Preparation

0.025 g CdO (99.998% purity Aldrich) and 0.033 g of ZnO (99.998% SigmaAldrich) were weighed into a three necked flask equipped with acondenser. To this was added: 2 ml tech grade oleic acid (Aldrich) and16 ml of tech grade octadecene (ODE) (Aldrich). The contents of theflask were degassed at 80° C. for 20 minutes in vacuo (200 millitorr).

Separately 0.032 g of sulfur (99.999% Strem) was dissolved in 10 ml oftech grade ODE in a septum capped vial by stirring and heating in an oilbath to 130° C. While the sample was heating up, the pressure of thevessel was reduced to 200 millitorr until the oil bath temperature was85° C., then further heating was continued under nitrogen. After 1 hour,when all the sulfur was dissolved, the sample was cooled to roomtemperature.

The contents of the three necked flask were stirred and heated to 310°C. under nitrogen until all the oxides dissolved to give a clearsolution. The temperature controller was then set to 300° C. and oncethe temperature stabilized at 300° C., approximately 4.0 ml of S in ODEwas rapidly injected. The temperature of the solution fell to about 270°C. and climbed back to 300° C. in ˜30 minutes. The reaction was stoppedafter 4 hours and the contents of the flask were transferred to adegassed vial under nitrogen and transferred to an inert atmosphere boxfor further purification.

The cores were purified by precipitation as follows. (In this example,the precipitation step was carried out two times for each sample.) Thesolution was divided in half; each half was added to a separatecentrifuge tube. Excess butanol (˜20-30 ml) was added to each centrifugetube. Each tube was then centrifuged for 5 min, 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. After mixing, each centrifuge tube was centrifugedagain. The supernatant liquid from each centrifuge tube was transferredto a separate clean tube; the solids in each centrifuge tube werediscarded. Cores were precipitated from the supernatant liquid in eachof the separate tubes by adding excess butanol (20-25 ml) with stirring.The new tubes containing the precipitated cores were centrifuged, thesupernatant liquid decanted, leaving precipitated cores in each tube.˜5-6 ml anhydrous hexane were added to the precipitated cores in eachtube to solvate the cores and the contents of each tube was filteredthrough a 0.2 micron filter. (The cores are in the filtrate.)

A 2.5 μl aliquot of the filtrate was diluted 100 fold with anhydroushexane and a UV VIS spectrum of the diluted aliquot was measured andabsorbance at 350 nm measured.

Characterization of the Cores:—first peak 460 nm, abs=0.0267, at 350 nm,abs=0.176

maximum peak emission—466 nm

FWHM 15 nm

Photoluminescence quantum efficiency ˜20%

Example 3B Shell Preparation (ZnS)

5 ml of 97% trioctylphosphine and 5 ml of oleylamine (distilled prior touse), were placed in a 4 necked flask equipped with a condenser andthermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N₂ to the flask and reducing the temperature to80° C., 4.5 ml of hexane containing core (see Example 1A above) wasadded and the solvent removed under vacuo for 2 hours. The temperaturewas raised to 170° C. and bis-trimethylsilylsulfide (49.6 mg) in 4 ml ofTOP and diethylzinc (17.2 mg) in 4 ml of TOP were added from separatesyringes at a rate of 50 microliters/minute. The solution in the flaskwas observed to develop a bluish color. After addition was complete, thesolution looked cloudy. The sample was transferred via a degassed vialinto an inert atmosphere box.

The cores including a ZnS shell were purified by precipitation asfollows. (In this example, the precipitation step was carried out twotimes for each sample.) The solution was divided into 2 centrifugetubes. Excess butanol (˜20-30 ml) was added to each centrifuge tube. Thecentrifuge tubes were centrifuged for 5 minutes at 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. Semiconductor nanocrystals comprising a core and a ZnSshell disposed over the core were precipitated by adding excess butanol(20-25 ml) with stirring. The centrifuge tube contents were centrifuged.The supernatant liquid was decanted, leaving the semiconductornanocrystals in the centrifuge tubes. ˜5 ml anhydrous hexane were addedto the semiconductor nanocrystals in one of the centrifuge tubes tosolvate the semiconductor nanocrystals. The hexane including thesolvated semiconductor nanocrystals was then transferred into the secondcentrifuge tube to solvate the semiconductor nanocrystals containedtherein. The mixture including the hexane and the semiconductornanocrystals from both centrifuge tubes was filtered through a 0.2micron filter. (The overcoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

maximum peak emission—470 nm

FWHM 17 nm

Photoluminescence quantum efficiency ˜59%

Example 4A Core Preparation

0.025 g CdO (99.998% Alfa) and 0.035 g of ZnO (99.999% Sigma Aldrich)were weighed into a three necked flask equipped with a condenser. Tothis was added: 2 ml tech grade oleic acid (Aldrich) and 16 ml of techgrade octadecene (ODE) (Aldrich). The content of the flask was degassedat 80° C. for 20 minutes in vacuo (200 millitorr).

Separately 0.035 g of sulfur (99.999% Strem) was dissolved in 10 ml oftech grade ODE in a septum capped vial by stirring and heating in an oilbath to 130° C. While the sample was heating up, the pressure of thevessel was reduced to 200 millitorr until the oil bath temperature was85° C., then further heating was continued under nitrogen. After 1 hour,when all the sulfur was dissolved, the sample was cooled to roomtemperature.

The contents of the three necked flask were stirred and heated to 310°C. under nitrogen until all the oxides dissolved to give a clearsolution. The temperature controller was then set to 300° C. and oncethe temperature stabilized at 300° C., approximately 4.0 ml of S in ODEwas rapidly injected. The temperature of the solution fell to about 270°C. and climbed back to 300° C. in ˜30 minutes. The reaction was stoppedafter 4 hours and the contents of the flask were transferred to adegassed vial under nitrogen and transferred to an inert atmosphere boxfor further purification.

The cores were purified by precipitation as follows. (In this example,the precipitation step was carried out two times for each sample.) Thesolution was divided in half; each half was added to a separatecentrifuge tube. Excess butanol (˜20-30 ml) was added to each centrifugetube. Each tube was then centrifuged for 5 min, 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. After mixing, each centrifuge tube was centrifugedagain. The supernatant liquid from each centrifuge tube was transferredto a separate clean tube; the solids in each centrifuge tube werediscarded. Cores were precipitated from the supernatant liquid in eachof the separate tubes by adding excess butanol (20-25 ml) with stirring.The new tubes containing the precipitated cores were centrifuged, thesupernatant liquid decanted, leaving precipitated cores in each tube.˜5-6 ml anhydrous hexane was added to the precipitated cores in eachtube to solvate the cores and the contents of each tube was filteredthrough a 0.2 micron filter. (The cores are in the filtrate.)

A 2.5 μl aliquot of the filtrate was diluted 100 fold with anhydroushexane and a UV VIS spectrum of the diluted aliquot was measured andabsorbance at 350 nm measured.

Characterization of the Cores:—first peak 454 nm, abs=0.11, at 350 nm,abs=0.652 maximum peak emission—459 nm

FWHM 16 nm

Photoluminescence quantum efficiency ˜28%

Example 4B Shell Preparation (ZnS)

5 ml of 97% trioctylphosphine and 5 ml of oleylamine (distilled prior touse), were placed in a 4 necked flask equipped with a condenser andthermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N2 to the flask and reducing the temperature to80° C., 2.4 ml of hexane containing core (see example 1 above) was addedand the solvent removed under vacuo for 2 hours. The temperature wasraised to 170° C. and bis-trimethylsilylsulfide (106.5 mg) in 4 ml ofTOP and diethylzinc (36.8 mg) in 4 ml of TOP were added from separatesyringes at 50 microliters/minute. The solution in the flask wasobserved to develop a bluish color and after addition was complete thesolution looked cloudy. The sample was transferred via a degassed vialinto an inert atmosphere box.

The cores including a ZnS shell were purified by precipitation asfollows. (In this example, the precipitation step was carried out twotimes for each sample.) The solution was divided into 2 centrifugetubes. Excess butanol (˜20-30 ml) was added to each centrifuge tube. Thecentrifuge tubes were centrifuged for 5 minutes at 4000 rpm. Aftercentrifuging, the supernatant liquid was poured off, retaining the solidin each centrifuge tube. ˜5 ml of hexane was added to the solid in eachcentrifuge tube and the contents of each centrifuge tube were mixedusing a vortexer. Semiconductor nanocrystals comprising a core and a ZnSshell disposed over the core were precipitated by adding excess butanol(20-25 ml) with stirring. The centrifuge tube contents were centrifuged.The supernatant liquid was decanted, leaving the semiconductornanocrystals in the centrifuge tubes. ˜5 ml anhydrous hexane were addedto the semiconductor nanocrystals in one of the centrifuge tubes tosolvate the semiconductor nanocrystals. The hexane including thesolvated semiconductor nanocrystals was then transferred into the secondcentrifuge tube to solvate the semiconductor nanocrystals containedtherein. The mixture including the hexane and the semiconductornanocrystals from both centrifuge tubes was filtered through a 0.2micron filter. (The overcoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

maximum peak emission—462 nm

FWHM 18 nm

Photoluminescence quantum efficiency ˜67%

Example 5A Core Preparation

0.050 g CdO (99.998% purity—Alfa) and 0.066 g of ZnO (99.999%purity—Sigma Aldrich) were weighed into a three necked flask equippedwith a condenser. To this was added: 4 ml tech grade oleic acid(Aldrich) and 32 ml of tech grade octadecene (ODE) (Aldrich). Thecontents of the flask were degassed at 80° C. for 20 minutes in vacuo(200 millitorr).

Separately 0.035 g of sulfur (99.999% Strem) was dissolved in 10 ml oftech grade ODE in a septum capped vial by stirring and heating in an oilbath to 130° C. While the sample was heating up, the pressure of thevessel was reduced to 200 millitorr until the oil bath temperature was85° C., then further heating was continued under nitrogen. After 1 hour,when all the sulfur was dissolved, the sample was cooled to roomtemperature.

The contents of the three necked flask were stirred and heated, undernitrogen, to 290° C. for 20 minutes then to 310° C., until all theoxides dissolved to give a clear solution. The temperature controllerwas then set to 300° C. and once the temperature stabilized at 300° C.,approximately 8.0 ml of S in ODE was rapidly injected. The temperatureof the solution fell to about 270° C. and climbed back to 300° C. in ˜30minutes. The reaction was stopped after 5 hours and the contents of theflask were transferred to a degassed vial under nitrogen and transferredto an inert atmosphere box for further purification.

The cores were purified by precipitation as follows. The solution wascentrifuged for 5 min, 4000 rpm. After centrifuging, the supernatantliquid was poured off, retaining the solid in the centrifuge tube. ˜10ml methanol was added to the tube and then decanted. ˜10 ml of anhydroushexane was thereafter added to the solid in the centrifuge tube and thecontents of the tube were mixed using a vortexer. After mixing, thecontents of the tube were centrifuged. The supernatant liquid wastransferred to a separate clean tube; the solids in the tube aftercentrifuging were discarded. Cores were precipitated from thesupernatant liquid by adding excess butanol (20-25 ml) with stirring.The tube containing the precipitated cores was centrifuged, thesupernatant liquid decanted, leaving precipitated cores in the tube.˜7.5 ml anhydrous hexane were added to the precipitated cores to solvatethe cores and the contents of the tube were filtered through a 0.2micron filter. (The cores are in the filtrate.)

A 2.5 μl aliquot of the filtrate was diluted 100 fold with anhydroushexane and a UV VIS spectrum of the diluted aliquot was measured andabsorbance at 350 nm measured.

Characterization of the Cores:

-   maximum peak emission—461 nm-   FWHM=14 nm-   Photoluminescence quantum efficiency=˜17%

Example 5B Shell Preparation (ZnS)

5 ml of 97% trioctylphosphine and 5 ml of oleylamine (distilled prior touse), were placed in a 4 necked flask equipped with a condenser andthermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N₂ to the flask and reducing the temperature to80° C., 3.8 ml of anhydrous hexane containing cores (see Example 5Aabove) was added and the solvent removed under vacuo for 2 hours. Thetemperature was raised to 170° C. and bis-trimethylsilylsulfide (92.53mg) in 4 ml of TOP and diethylzinc (32.00 mg) in 4 ml of TOP were addedfrom separate syringes at a rate of 50 microliters/minute. The solutionin the flask was observed to develop a bluish color. After addition wascomplete, the solution looked cloudy. The sample was transferred via adegassed vial into an inert atmosphere box.

The cores including a ZnS shell were purified by precipitation asfollows. The sample was transferred to Tube 1 and centrifuged for 5minutes at 4000 rpm. Tube 1 (Batch 1):

After centrifuging, the supernatant liquid was poured off into Tube 2,retaining the solid in Tube 1. ˜5 ml of anhydrous hexane was added tothe solid in centrifuge Tube 1 and the contents were mixed using avortexer. Semiconductor nanocrystals comprising a core and a ZnS shelldisposed over the core were precipitated by adding excess butanol (20-25ml) with stirring. The Tube 1 contents were centrifuged. The supernatantliquid was decanted, leaving the semiconductor nanocrystals in thecentrifuge tubes. ˜3 ml anhydrous hexane were added to the semiconductornanocrystals in Tube 1 to solvate the semiconductor nanocrystals. Themixture including the anhydrous hexane and the semiconductornanocrystals from centrifuge tube 1 was filtered through a 0.2 micronfilter. (The overcoated cores are in the filtrate.)

Tube 2 (Batch 2):

Excess butanol (˜20-30 ml) was added to Tube 2. Tube 2 was centrifugedfor 5 minutes at 4000 rpm. After centrifuging, the supernatant liquidwas poured off, retaining the solid in the centrifuge tube. ˜5 ml ofanhydrous hexane was added to the solid in each centrifuge tube and thecontents of each centrifuge tube were mixed using a vortexer.Semiconductor nanocrystals comprising a core and a ZnS shell disposedover the core were precipitated by adding excess butanol (20-25 ml) withstirring. The centrifuge tube contents were centrifuged. The supernatantliquid was decanted, leaving the semiconductor nanocrystals in thecentrifuge tubes. ˜3 ml anhydrous hexane were added to the semiconductornanocrystals in one of the centrifuge tubes to solvate the semiconductornanocrystals. The mixture including the anhydrous hexane and thesemiconductor nanocrystals from both centrifuge tubes was filteredthrough a 0.2 micron filter. (The overcoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

-   maximum peak emission 463 nm-   FWHM=18 nm-   Photoluminescence quantum efficiency ˜100%—(Batches 1 & 2)

Example 5C Shell Preparation in TOPO

5 grams of 99% trioctylphosphine oxide and 5 ml of oleylamine (distilledprior to use), were placed in a 4 necked flask equipped with a condenserand thermocouple. The sample was stirred and degassed at 100° C. for ˜1hour. After introducing N₂ to the flask and reducing the temperature to80° C., 3.8 ml of anhydrous hexane containing cores (see Example 5Aabove) was added and the solvent removed under vacuo for 2 hours. Thetemperature was raised to 170° C. and bis-trimethylsilylsulfide (92.53mg) in 4 ml of TOP and diethylzinc (32.00 mg) in 4 ml of TOP were addedfrom separate syringes at a rate of 50 microliters/minute. The solutionin the flask was observed to develop a yellow-green color. Afteraddition was complete, the solution looked cloudy. The sample wastransferred via a degassed vial into an inert atmosphere box.

The cores including a ZnS shell prepared in TOPO were purified byprecipitation as follows. (In this example, the precipitation step wascarried out two times for each sample) as follows. ˜5 ml of anhydroushexane was added to the solid in the degassed vial and 5 ml of solutionwas added to each of two tubes. Semiconductor nanocrystals comprising acore and a ZnS shell disposed over the core were precipitated by adding20 ml of a 3:1 anhydrous methanol/isopropanol mixture to each of the twotubes, following which the supernatant liquid was decanted, leaving thesemiconductor nanocrystals in the centrifuge tubes. ˜3 ml anhydroushexane were added to the semiconductor nanocrystals in each of thecentrifuge tubes to solvate the semiconductor nanocrystals, which werethen re-precipitated by the addition of 5 ml of a 3:1 anhydrousmethanol/isopropanol mixture. The re-precipitated semiconductornanocrystals were centrifuged to separate and recover the nanocrystals.After the supernatant liquid was removed, the nanocrystals were solvatedin 3 ml anhydrous hexane. The mixture including the anhydrous hexane andthe semiconductor nanocrystals from both centrifuge tubes was filteredthrough a 0.2 micron filter. (The overcoated cores are in the filtrate.)

Characterization of the Core/Shell Nanocrystals:

-   maximum peak emission 464 nm-   FWHM=18-   Photoluminescence quantum efficiency 79%

The Zn_(x)Cd_(1−x)S cores prepared in Examples 1A, 2A, and 3Ademonstrate a maximum peak emission at a wavelength in a range fromabout 433 to about 478 nm and a FWHM in a range from about 14 to about18 nm. The photoluminescence quantum efficiencies for the cores preparedin Examples 1A, 2A, and 3A (under nitrogen varied) range from about 20%to about 40%. For these core samples, the measured photoluminescencequantum yield increased with zinc content. Additionally, the maximumpeak emission demonstrated a blue shift as more zinc was incorporated inthe core. This is consistent with an alloyed composition.

After overcoating the cores with ZnS by a suitable overcoating process(such as, for example, that described above), the photoluminescencequantum efficiency of the ZnS treated cores increased from about 20-50%(for the cores alone) to from about 59 to about 100%.

The ZnS treated cores are believed to have a core/shell structure basedon the observation of a red shift of the maximum peak emission of theZnS treated cores compared to the cores that have not undergone theovercoating process.

Examples 1-5 Determination of Photoluminescence Quantum Efficiency(PLQE)

Diphenyl anthracene (DPA) was used to prepare standards of variousconcentrations by dissolving DPA in cyclohexane in amounts appropriateto prepare the desired concentrations. The absorbance of each of thestandards was measured at 373 nm, and the emission area was measuredafter excitation at 373 nm. For example, a series of standards ofvarying concentrations were prepared as described above and thefollowing absorbance values were obtained for the standards at 373 nm:0.135, 0.074, 0.044 and 0.023. A straight line was plotted betweenemission and absorbance to get a slope. The slope obtained from astraight line plot of the four absorbance measurements listed above was˜73661 arbitrary units. The measurements were made on a CARY Eclipsespectrophotometer. The CARY Eclipse settings used when taking themeasurements were:

Data mode Fluorescence Scan mode Emission X Mode Wavelength (nm) Start(nm) 383.00 Stop (nm) 700.00 Ex. Wavelength (nm) 373.00 Ex. Slit (nm)2.5 Em. Slit (nm) 2.5 Scan rate (nm/min) 600.00 Data interval (nm)1.0000 Averaging Time (s) 0.1000 Excitation filter Auto Emission filterOpen PMT voltage (V) Medium Corrected spectra OFF

Other settings can be used and can be readily determined by one ofordinary skill in the art. Other brand spectrophotometers can be used tomeasure PL quantum efficiency and the settings to be used can be readilydetermined by one of ordinary skill in the art.

Example 6A Synthesis of CdZnSe Nanocrystal Core (1:30:60 Cd:Zn:Se ratio)

10 mg CdO (F.W.=128.41) (99.998% purity—Alfa) (0.077 mmol Cd) and 50 mgOctylphosphonic Acid (F.W.=194.2; Poly Carbon Industries) are added to a50 ml three necked round bottom flask and attached to a vacuum line.11.25 mL of Octadecene (ODE) is added to the 50 ml round bottom flaskusing a 20 mL syringe equipped with blunt needle—(Fluka 95%) and 3.75 mLof Oleylamine (also known as 1-Amino-9-octadecene) is added to the 50 mlbottom flask using a 5 mL syringe equipped with blunt needle. (Theoleylamine is vacuum distilled prior to use.) The mixture is degassed at100° C. for ˜1 hr. The flask is then heated to 310° C. until the mixtureturns clear (Cd phosphonate is formed). Once the solution is clear, thesolution temperature is dropped to 120° C. and degassed for another fewcycles of evacuate/refill with N₂.

1.3 mL Octadecene (ODE), 4.7 mL of TOPSe (1M) (4.7 mmol Se), and 288 mgZnEt₂ (F.W.=123.49) (2.34 mmol Zn) are placed into a 20 mL vial in anitrogen glove box. The solution is mixed and drawn into one 10 mLsyringe and removed from the glove box.

The Cd-containing solution in the 50 ml three neck round bottom flask isheated to 305° C. and the Zn and Se containing solution is rapidlyinjected into the pot using the large stainless steel syringe needles.The reaction is allowed to run overnight at 290° C. for approximately 16hrs. (The reaction can also be run for longer times, e.g., 25 hours orlonger.)

After 16 hours, the absorbance should be about 418 nm and a FWHM of 25nm can be obtained.

Clean Up of Nanocrystal Cores:

The crude nanocrystal cores are further processed in a glove boxenvironment. About 2.5-3 ml (about 0.05 mmol) of the crude core growthsolution is added to a 50 ml centrifuge tube. Excess butanol (about 30ml) is slowly added to the tube while stirring. About 10 ml methanol isthen slowly added to the tube while stirring. The mixture is vortexes toensure thorough washing and mixing and to separate the nanocrystalcores. The supernatant is poured off, and the nanocrystal cores aredispersed in 2-4 ml hexane. The mixture is filtered and the nanocrystalcores are diluted 100 fold. Preferably, concentrated hexane iscompletely degassed prior to being injected into the pot mixture.Recovery of nanocrystal cores from the supernatant can be increased byadding additional MeOH and Butanol.

Example 6B Overcoating the CdZnSe Cores Prepared in Example 6A

Three mL syringes are prepared in the glove box with the precursors forthe shell:

The first syringe: about 11 mg of CdMe₂; and 1 mL of TOP.

The second syringe: 77 mg of ZnEt₂ and 3 mL of TOP.

The third syringe: 230 mg of (TMS)₂S and 3 mL of TOP.

The shell precursor mixture for each syringe is prepared by placing theTri-n-octylphosphine (TOP) into an 8 mL glass vial. The precursors(dimethylcadmium, diethylzinc (ZnEt₂) and Bis(TMS)sulfide ((TMS)₂S)) arethen dripped into the Tri-n-octylphosphine using a syringe until theright weight of material has been added to each vial. The solution ismixed gently with the vial capped and then drawn up into the 5 mLsyringe. The amounts of precursors are calculated based on approximately5 monolayers including 30% Cd and about 8 monolayers of ZnS, regardlessof the actual shell composition and structure.

Micro capillary tubing is then loaded onto each syringe and a smallamount of solution is pushed through to clear the tubing of nitrogen(this is all done inside the glove box).

Ten (10) grams of Tri-n-octylphosphine oxide (TOPO) (99% Strem) and 0.8grams of octadecylphosphonic acid (ODPA) (Polycarbon Industries) areadded to a 4 neck 50 mL round bottom flask including a football-shapedmagnetic stirrer bar. The flask is also equipped with a rubber septum ontwo of the four necks, a distillation column on the middle neck and thetemperature probe in the last neck. The contents of the flask are heatedto about 120° C. while under nitrogen. When the temperature reachesabout 120° C., the nitrogen line is closed, and the flask is slowlyopened up to vacuum. The contents of the flask are degassed under vacuumat 120° C. for roughly 1.5 hours. When the solution in the round bottomflask has finished degassing, the vacuum is closed and the flask isopened up to nitrogen. The temperature of the flask is set to 80° C. Thecores prepared as described in Example 1A in hexane are added to theround bottom flask using a 5 mL syringe. The vacuum is slowly opened upand all of the hexane is removed from the flask, leaving behind thecores (this can take as long as 2 hours). When all of the hexane hasbeen removed, the vacuum is closed and the flask is opened up tonitrogen and the temperature brought down to 80° C. Approximately 15 minprior to introducing the shell precursors, about 0.48 ml of decylamine(DA). (using 1 ml syringe) is added and the temperature is increased to170° C. under nitrogen. Once the temperature of the flask reaches 170°C., the syringes are loaded into syringe pumps to introduce the threelines into the flask (one going through each septum, so that the microcapillary tubing is hugging the flask wall and about 0.5 cm submergedinto the stirring solution).

With the flask at 170° C., the syringe pumps are turned on and the threesolutions are pumped into the flask at a rate of 50 μL/min. with rapidstirring. All of the Cd-precursor is added in about 20 minutes (duringwhich time Zn-precursor and S-precursor are also added) Zn-precursor andS-precursor additions continue over another 40 minutes. Optionally, whenall of the overcoating solutions from the three syringes has been addedto the flask, the syringe pump lines are removed from the flask, thetemperature is turned down to 100° C., and 10 ml of toluene is added andallowed to sit overnight under nitrogen.

Results/Characterization:

Crude mixture for this core/shell composition and structure should havean emission maximum of approximately 460 nm with a FWHM of ˜30 nm.

Clean Up of Core-Shell Particles:

The total growth solution is divided into two aliquots, each being putinto a 50 mL centrifuge tube. 2 ml of hexane is added to each andstirred, followed by an addition of 2 ml of butanol to each andstirring. An excess ˜20 ml of methanol is added to each centrifuge tubewith stirring. The centrifuge tubes are centrifuged 5 minutes at about3900 rpm. The particles in each tube are dispersed in about 10 ml ofhexane with stirring using a vortexer. The centrifuge tubes are thencentrifuged for 5 minutes at about 3900 rpm. The supernatant includesthe hexane and the overcoated cores. The supernatant is collected fromeach tube and is placed into another two centrifuge tubes. (The solid isa salt that has formed and is waste.) The hexane/overcoated coresupernatant is filtered using a 0.2 μm syringe filter. A small amount ofbutanol (˜1 m) is added to each tube and stirred well, followed by anaddition of enough methanol to each tube to cause the solution to becomecloudy (˜8 mL). An additional ˜5 mL of methanol is added to each tubeafter reaching the cloudy point. The tubes are centrifuged for 5 minutesat about 3900 rpm. The supernatant is poured off. The purifiedovercoated cores are now at the bottom of the tube and the supernatantis waste. The overcoated cores are dispersed in a minimal amount ofchloroform (˜2-4 mL) (preferably anhydrous). The overcoatedcores/chloroform dispersion is filtered with a 0.2 micron syringefilter. The filtered overcoated cores/chloroform dispersion is placedinto an 8 or 20 mL vial.

Results/Characterization:

The cleaned-up core/shell dispersion in chloroform can have an emissionmaximum of approximately 460 nm with a FWHM of ˜26 nm.

Examples 7-11

The following overcoating examples 7-11 were carried out using coresprepared substantially in accordance with the procedure of Example 6A.

The shell overcoating procedure for each example was carried outsubstantially as described in Example 6B with the ingredients andprecursors listed below; each listed ingredient or precursor being usedin amounts approximating those given for the same ingredients andprecursors in Examples 6B. (If any reagent or precursor included inExamples 6B was not included in any of Examples 7-11, it is not listed.)

RESULTS 4 NECK 50 ml Emission Maximum ROUND BOTTOM (FWHM) EXAM- FLASKSHELL Solution Quantum PLE INGREDIENTS PRECURSORS Yield, QY 7 CoreCd-precursor 460 nm (FWHM = 31), ODPA Zn-precursor QY 70%, 60% (The DAS-precursor overcoated cores were cleaned up 4 times) 8 CoreCd-precursor 464 nm (FWHM = 37) ODPA Zn-precursor (The overcoated coresS-precursor were cleaned up 2 times) QY 55% (under N₂), 32% (afteropening to air) The overcoated cores were cleaned up 2 times) 9 CoreCd-precursor 433 nm (FWHM = 25) DA Zn-precursor QY 10% (after openingS-precursor to air) The overcoated cores were cleaned up 2 times) 10Core (FWHJ = 421) Cd-precursor 465 nm (FWHM = 40) ODPA S-precursor QY29% DA The overcoated cores were cleaned up 2 times) 11 Core (FWHM =Zn-precursor 419 nm (FWHM = 27) 421) S-precursor QY 26% ODPA Theovercoated cores DA were cleaned up 2 times)

Examples 6-11 Determination of Photoluminescence Quantum Efficiency(PLQE)

Diphenyl anthracene (DPA) is used to prepare standards of variousconcentrations by dissolving DPA in cyclohexane in amounts appropriateto prepare the desired concentrations. The absorbance of each of thestandards is measured at 373 nm, and the emission area is measured afterexcitation at 373 nm. For example, a series of standards of varyingconcentrations were prepared as described above and the followingabsorbance values were obtained for the standards at 373 nm: 0.135,0.074, 0.044 and 0.023. A straight line was plotted between emission andabsorbance to get a slope. The slope obtained from a straight line plotof the four absorbance measurements listed above was ˜73661 units. Themeasurements were made on a CARY Eclipse spectrophotometer. The CARYEclipse settings used when taking the measurements were:

Data mode Fluorescence Scan mode Emission X Mode Wavelength (nm) Start(nm) 383.00 Stop (nm) 700.00 Ex. Wavelength (nm) 373.00 Ex. Slit (nm)2.5 Em. Slit (nm) 2.5 Scan rate (nm/min) 600.00 Data interval (nm)1.0000 Averaging Time (s) 0.1000 Excitation filter Auto Emission filterOpen PMT voltage (V) Medium Corrected spectra OFF

Other settings can be used and can be readily determined by one ofordinary skill in the art. Other brand spectrophotometers can be used tomeasure PL quantum efficiency and the settings to be used can be readilydetermined by one of ordinary skill in the art.

Semiconductor nanocrystals for which the % photoluminescence quantumefficiency is to be measured are dispersed in hexane and the absorbanceat 373 nm is measured. The sample is excited at 373 nm using the sameconditions as the standard and the emission area is measured.

Photoluminescence quantum yield can be calculated using the followingequation:PLQE={[maximum peak emission area of semiconductornanocrystal×0.90×(1.375)²]}/{[slope of line plot forstandards×absorbance of semiconductor nanocrystal at 373 nm×(1.423)²]}

wherein, 0.90 is the PLQE of the standard used (DPA); 1.375 is therefractive index of hexane, 1.423 is the refractive index ofcyclohexane,

% Photoluminescence quantum yield can be calculated from the PLQE valueusing the following equation:% PLQE=100×PLQE.

Preferably, the standard comprises an organic dye the photoluminescencespectrum of which overlaps significantly with that of the semiconductornanocrystal sample. The standard samples and the semiconductornanocrystal sample(s) are measured under the same settings of thespectrophotometer.

Semiconductor nanocrystals show strong quantum confinement effects thatcan be harnessed in designing bottom-up chemical approaches to createcomplex heterostructures with electronic and optical properties that aretunable with the size and composition of the semiconductor nanocrystals.

When an electron and hole localize on a semiconductor nanocrystal,emission can occur at an emission wavelength. The emission has afrequency that corresponds to the band gap of the quantum confinedsemiconductor material. The band gap is a function of the size of thesemiconductor nanocrystal. Semiconductor nanocrystals having smalldiameters can have properties intermediate between molecular and bulkforms of matter. For example, semiconductor nanocrystals based onsemiconductor materials having small diameters can exhibit quantumconfinement of both the electron and hole in all three dimensions, whichleads to an increase in the effective band gap of the material withdecreasing nanocrystal size. Consequently, both the optical absorptionand emission of semiconductor nanocrystals shift to the blue, or tohigher energies, as the size of the nanocrystal decreases.

The emission from a semiconductor nanocrystal can be a narrow Gaussianemission band that can be tuned through the complete wavelength range ofthe ultraviolet, visible, or infra-red regions of the spectrum byvarying the size of the semiconductor nanocrystal, the composition ofthe semiconductor nanocrystal, or both. For example, CdSe can be tunedin the visible region and InAs can be tuned in the infra-red region.

In certain embodiments, a population of semiconductor nanocrystals canhave a narrow size distribution that can result in emission of light ina narrow spectral range, The population can be monodisperse preferablyexhibits less than a 15% rms (root-mean-square) deviation in diameter ofthe semiconductor nanocrystals, more preferably less than 10%, mostpreferably less than 5%. In certain embodiments, spectral emissions in anarrow range of not greater than about 75 nm, more preferably notgreater than about 60 nm, still more preferably not greater than about40 nm, and most preferably not greater than about 30 nm full width athalf max (FWHM) for semiconductor nanocrystals that emit in the visiblecan be observed. IR-emitting semiconductor nanocrystals preferably havea FWHM of not greater than about 150 nm, or more preferably not greaterthan about 100 nm. In certain embodiments, expressed in terms of theenergy of the emission, an emission can have a FWHM of not greater than0.05 eV, or not greater than 0.03 eV. The breadth of the emissiondecreases as the dispersity of semiconductor nanocrystal diametersdecreases.

The narrow FWHM of semiconductor nanocrystals can result in saturatedcolor emission. This can lead to efficient lighting devices even in thered and blue parts of the visible spectrum, since in semiconductornanocrystal emitting devices no photons are lost to infra-red and UVemission. The broadly tunable, saturated color emission over the entirevisible spectrum of a single material system is unmatched by any classof organic chromophores (see, for example, Dabbousi et al., J. Phys.Chem. 101, 9463 (1997), which is incorporated by reference in itsentirety). A monodisperse population of semiconductor nanocrystals willemit light spanning a narrow range of wavelengths. A device includingsemiconductor nanocrystals of different compositions, sizes, and/orstructures can emit light in more than one narrow range of wavelengths.The color of emitted light perceived by a viewer can be controlled byselecting appropriate combinations of semiconductor nanocrystal sizesand materials in the device as well as relative subpixel currents. Thedegeneracy of the band edge energy levels of semiconductor nanocrystalsfacilitates capture and radiative recombination of all possibleexcitons, whether generated by direct charge injection or energytransfer. The maximum theoretical semiconductor nanocrystal lightingdevice efficiencies are therefore comparable to the unity efficiency ofphosphorescent organic light-emitting devices. The excited statelifetime (τ) of the semiconductor nanocrystal is much shorter (τ˜10 ns)than a typical phosphor (τ>0.1 μs), enabling semiconductor nanocrystallighting devices to operate efficiently even at high current density andhigh brightness.

Semiconductor nanocrystals can be suitable for a variety ofapplications, including those disclosed in U.S. patent application Ser.No. 09/156,863, filed Sep. 18, 1998 (now U.S. Pat. No. 6,251,303), Ser.No. 09/160,454, filed Sep. 24, 1998 (now U.S. Pat. No. 6,326,144), Ser.No. 09/160,458, filed Sep. 24, 1998 (now U.S. Pat. No. 6,617,583), Ser.No. 09/350,956, filed Jul. 9, 1999 (now U.S. Pat. No. 6,803,719), andSer. No. 10/400,908, filed Mar. 28, 2003 (U.S. Published PatentApplication No. 20040023010), all of which are incorporated herein byreference in their entirety.

For example, the nanocrystals can be used in a variety of end-useapplications and products. Such end-use applications and productinclude, but are not limited to, optoelectronic devices including lightemitting diodes (LEDs) or alternating current devices (ACTFELDs),lasers, biomedical tags, photoelectric devices, solar cells, catalysts,and the like. Light-emitting devices including nanocrystals inaccordance with the present invention may be incorporated into a widevariety of consumer products, including, but not limited to, flat paneldisplays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control such devices,including passive matrix and active matrix.

Light-emitting devices including semiconductor nanocrystals can be madeby spin-casting a solution containing the hole transport layer (HTL)organic semiconductor molecules and the semiconductor nanocrystals,where the HTL forms underneath the semiconductor nanocrystal layer viaphase separation (see, for example, U.S. patent application Ser. No.10/400,907 (now U.S. Pat. No. 7,332,211) and Ser. No. 10/400,908 (nowU.S. Pat. No. 7,700,200), both filed Mar. 28, 2003, each of which isincorporated by reference in its entirety). In certain embodiments, thisphase separation technique can be used to place a monolayer ofsemiconductor nanocrystals between an organic semiconductor HTL andelectron transport layer (ETL), thereby effectively exploiting thefavorable light emission properties of semiconductor nanocrystals, whileminimizing their impact on electrical performance. Other techniques fordepositing semiconductor nanocrystals include Langmuir-Blodgetttechniques and drop-casting. Some techniques for depositingsemiconductor nanocrystals may not be well suited for all possiblesubstrate materials, may involve use of chemicals that can affect theelectrical or optical properties of the layer, may subject the substrateto harsh conditions, and/or may place constraints on the types ofdevices that can be grown in some way. Other techniques discussed belowmay be preferable if a patterned layer of semiconductor nanocrystals isdesired.

Preferably, semiconductor nanocrystals are processed in a controlled(oxygen-free and moisture-free) environment, preventing the quenching ofluminescent efficiency during the fabrication process.

In certain embodiments, semiconductor nanocrystals can be deposited in apatterned arrangement. Patterned semiconductor nanocrystals can be usedto form an array of pixels comprising, e.g., red, green, and blue oralternatively, red, yellow, green, blue-green, and/or blue emitting, orother combinations of distinguishable color emitting subpixels, that areenergized to produce light of a predetermined wavelength.

An example of a technique for depositing a light-emitting materialcomprising semiconductor nanocrystals in a pattern and/or in amulti-color pattern or other array is contact printing. Contact printingadvantageously allows micron-scale (e.g., less than 1 mm, less than 500microns, less than 200 microns, less than 100 microns, less than 50microns, less than 25 microns, or less than 10 microns) patterning offeatures on a surface. Pattern features can also be applied at largerscales, such as 1 mm or greater, 1 cm or greater, 1 m or greater, 10 mor greater. Contact printing can allow dry (e.g., liquid free orsubstantially liquid free) application of a patterned semiconductornanocrystal layer to a surface. In a pixilated device, the semiconductornanocrystal layer comprises a patterned array of the semiconductornanocrystals on the underlying layer. In instances where a pixelincludes subpixels, the sizes of the subpixels can be a proportionatefraction of the pixel size, based on the number of subpixels.

Additional information and methods for depositing semiconductornanocrystals are described in U.S. patent application Ser. No.11/253,612 entitled “Method And System For Transferring A PatternedMaterial”, filed 20 Oct. 2005 (U.S. Published Application No.20060196375A1), and Ser. No. 11/253,595 entitled “Light Emitting DeviceIncluding Semiconductor Nanocrystals”, filed 20 Oct. 2005 (U.S.Published Application No. 20080001167A1), each of which is herebyincorporated herein by reference in its entirety.

Other materials, techniques, methods, applications, and information thatmay be useful with the present invention are described in, U.S.Provisional Patent Application No. 60/792,170, of Seth Coe-Sullivan, etal., for “Composition Including Material, Methods Of DepositingMaterial, Articles Including Same And Systems For Depositing Material”,filed on 14 Apr. 2006; U.S. Provisional Patent Application No.60/792,084, of Maria J. Anc, for “Methods Of Depositing Material,Methods Of Making A Device, And System”, filed on 14 Apr. 2006, U.S.Provisional Patent Application No. 60/792,086, of Marshall Cox, et al,for “Methods Of Depositing Nanomaterial & Methods Of Making A Device”filed on 14 Apr. 2006; U.S. Provisional Patent Application No.60/792,167 of Seth Coe-Sullivan, et al, for “Articles For DepositingMaterials, Transfer Surfaces, And Methods” filed on 14 Apr. 2006, U.S.Provisional Patent Application No. 60/792,083 of LeeAnn Kim et al., for“Applicator For Depositing Materials And Methods” filed on 14 Apr. 2006;U.S. Provisional Patent Application 60/793,990 of LeeAnn Kim et al., for“Applicator For Depositing Materials And Methods” filed by Express Mailon 21 Apr. 2006; U.S. Provisional Patent Application No. 60/790,393 ofSeth Coe-Sullivan et al., for “Methods And Articles IncludingNanomaterial”, filed on 7 Apr. 2006; U.S. Provisional Patent ApplicationNo. 60/805,735 of Seth Coe-Sullivan, for “Methods For DepositingNanomaterial, Methods For Fabricating A Device, And Methods ForFabricating An Array Of Devices”, filed on 24 Jun. 2006; U.S.Provisional Patent Application No. 60/805,736 of Seth Coe-Sullivan etal., for “Methods For Depositing Nanomaterial, Methods For Fabricating ADevice, Methods For Fabricating An Array Of Devices And Compositions”,filed on 24 Jun. 2006; U.S. Provisional Patent Application No.60/805,738 of Seth Coe-Sullivan et al., for “Methods And ArticlesIncluding Nanomaterial”, filed on 24 Jun. 2006; U.S, Provisional PatentApplication No, 60/795,420 of Paul Beatty et al., for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed on 27 Apr. 2006; U.S. Provisional PatentApplication No. 60/804,921 of Seth Coe-Sullivan et al., for“Light-Emitting Devices And Displays With Improved Performance”, filedon 15 Jun. 2006, U.S. patent application Ser. No. 11/071,244 of JonathanS. Steckel et al. (now U.S. Pat. No. 7,253,452), for “Blue LightEmitting Semiconductor Nanocrystal Materials” 4 Mar. 2005 (includingU.S. Patent Application No. 60/550,314, filed on 8 Mar. 2004, from whichit claims priority), U.S. Provisional Patent Application No. 60/825,373,filed 12 Sep. 2006, of Seth A. Coe-Sullivan et al., for “Light-EmittingDevices And Displays With Improved Performance”; and U.S. ProvisionalPatent Application No. 60/825,374, filed 12 Sep. 2006, of Seth A.Coe-Sullivan et al., for “Light-Emitting Devices And Displays WithImproved Performance”. The disclosures of each of the foregoing listedpatent documents are hereby incorporated herein by reference in theirentireties.

Other multilayer structures may optionally be used to improve theperformance (see, for example, U.S. patent application Ser. No.10/400,907 (now U.S. Pat. No. 7,332,211) and Ser No. 10/400,908, filedMar. 28, 2003 (now U.S. Pat. No. 7,700,200), each of which isincorporated herein by reference in its entirety) of the light-emittingdevices and displays of the invention.

The performance of light emitting devices can be improved by increasingtheir efficiency, narrowing or broadening their emission spectra, orpolarizing their emission. See, for example, Bulovic et al.,Semiconductors and Semimetals 64, 255 (2000), Adachi et al., Appl. Phys.Lett. 78, 1622 (2001), Yamasaki et al., Appl. Phys. Lett. 76, 1243(2000), Dirr et al., Jpn. J. Appl. Phys. 37, 1457 (1998), and D'Andradeet al., MRS Fall Meeting, BB6.2 (2001), each of which is incorporatedherein by reference in its entirety. Semiconductor nanocrystals can beincluded in efficient hybrid organic/inorganic light emitting devices.

Because of the diversity of semiconductor nanocrystal materials that canbe prepared, and the wavelength tuning via semiconductor nanocrystalcomposition, structure, and size, devices that are capable of emittinglight of a predetermined color are possible with use of semiconductornanocrystals as the emissive material. Semiconductor nanocrystallight-emitted devices can be tuned to emit anywhere in the spectrum.

The size and material of a semiconductor nanocrystal can be selectedsuch that the semiconductor nanocrystal emits light having apredetermined wavelength.

Individual light-emitting devices can be formed. In other embodiments, aplurality of individual light-emitting devices can be formed at multiplelocations on a single substrate to form a display. A display can includea light-emitting device in accordance with the present invention and oneor more additional devices that emit at the same or differentwavelengths. By patterning the substrate with arrays of differentcolor-emitting semiconductor nanocrystals, a display including pixels ofdifferent colors can be formed.

An individual light-emitting device or one or more light-emittingdevices of a display can optionally include a mixture of differentcolor-emitting semiconductor nanocrystals formulated to produce a whitelight. White light can alternatively be produced from a device includingred, green, blue, and, optionally, additional color-emitting pixels.

Examples of other displays are included in U.S. Patent Application No.60/771,643 for “Displays Including Semiconductor Nanocrystals AndMethods Of Making Same”, of Seth Coe-Sullivan et al., filed 9 Feb. 2006,the disclosure of which is hereby incorporated herein by reference inits entirety.

For additional information relating to semiconductor nanocrystals andtheir use, see also U.S. Patent Application Nos. 60/620,967, filed Oct.22, 2004, and Ser. No. 11/032,163, filed Jan. 11, 2005 (now U.S. Pat.No. 8,134,175), U.S. patent application Ser. No. 11/071,244, filed 4Mar. 2005 (now U.S. Pat. No. 7,253,452). Each of the foregoing patentapplications is hereby incorporated herein by reference in its entirety.

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Thus, for example,reference to an emissive material includes reference to one or more ofsuch materials.

When an amount, concentration, or other value or parameter is given aseither a range, preferred range, or a list of upper preferable valuesand lower preferable values, this is to be understood as specificallydisclosing all ranges formed from any pair of any upper range limit orpreferred value and any lower range limit or preferred value, regardlessof whether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding equivalents of thefeatures shown and described, or portions thereof, it being recognizedthat various modifications are possible within the scope of theinvention claimed. Moreover, any one or more features of any embodimentof the invention may be combined with any one or more other features ofany other embodiment of the invention, without departing from the scopeof the invention. Additional embodiments of the present invention willalso be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly, with a true scope and spirit of the invention being indicated bythe following claims and equivalents thereof.

All patents, patent applications, and publications mentioned above areherein incorporated by reference in their entirety for all purposes.None of the patents, patent applications, and publications mentionedabove are admitted to be prior art.

What is claimed is:
 1. A device comprising a semiconductor nanocrystalcapable of emitting blue light including a maximum peak emission at awavelength not greater than about 470 nm with a photoluminescencequantum efficiency greater than about 65% upon excitation, thesemiconductor nanocrystal comprising a core/shell structure wherein thecore comprises a first semiconductor material and the shell comprises asecond semiconductor material, wherein the shell is disposed over atleast a portion of a surface of the core.
 2. A device in accordance withclaim 1 wherein the semiconductor nanocrystal is capable of emittinglight with a photoluminescence quantum efficiency greater than about 70%upon excitation.
 3. A device in accordance with claim 1 wherein thesemiconductor nanocrystal is capable of emitting light with aphotoluminescence quantum efficiency greater than about 80% uponexcitation.
 4. A device in accordance with claim 1 wherein thesemiconductor nanocrystal is capable of emitting light with aphotoluminescence quantum efficiency greater than about 90% uponexcitation.
 5. A device including a semiconductor nanocrystal includinga core comprising a first semiconductor material comprising at leastthree chemical elements and a shell disposed over at least a portion ofthe core, the shell comprising a second semiconductor material, whereinthe semiconductor nanocrystal is capable of emitting blue light with aphotoluminescence quantum efficiency greater than about 65% uponexcitation.
 6. A device in accordance with claim 5 wherein the devicecomprises a light-emitting device.
 7. A device in accordance with claim5 wherein the first semiconductor material comprises zinc, cadmium, andselenium.
 8. A semiconductor nanocrystal in accordance with claim 7,wherein the second semiconductor material comprises Cd_(x)Zn_(1−x)Swherein 0<x<1.
 9. A device in accordance with claim 5 wherein the secondsemiconductor material comprises zinc, cadmium, and sulfur.
 10. A devicein accordance with claim 5 wherein the first semiconductor materialcomprises Zn_(1−x)Cd_(x)Se, wherein 0<x<1.
 11. A device in accordancewith claim 5 wherein the second semiconductor material comprisesCd_(x)Zn_(1−x)S wherein 0<x<1.
 12. A device in accordance with claim 5wherein the first semiconductor material comprises zinc, cadmium, andsulfur.
 13. A device in accordance with claim 5 wherein the secondsemiconductor material comprises zinc and sulfur.
 14. A device inaccordance with claim 5 wherein the first semiconductor materialcomprises Zn_(x)Cd_(1−x)S, wherein 0<x<1.
 15. A device in accordancewith claim 14 wherein 0<x<0.5.
 16. A device in accordance with claim 14wherein 0.05<x<0.2.
 17. A device in accordance with claim 5 wherein thesecond semiconductor material comprises ZnS.
 18. A device in accordancewith claim 5 wherein the device is a light-emitting device.
 19. A devicecomprising a layer comprising a plurality of semiconductor nanocrystalsand means for exciting the semiconductor nanocrystals, wherein at leasta portion of the semiconductor nanocrystals comprise a semiconductornanocrystal including a core comprising a first semiconductor materialcomprising at least three chemical elements and a shell disposed over atleast a portion of the core, the shell comprising a second semiconductormaterial, wherein the semiconductor nanocrystal is capable of emittingblue light with a photoluminescence quantum efficiency greater thanabout 65% upon excitation.
 20. A device in accordance with claim 19wherein the means for exciting the semiconductor nanocrystals comprisesa light source.
 21. A device in accordance with claim 19 wherein themeans for exciting the semiconductor nanocrystals comprises a firstelectrode disposed on a substrate and a second electrode opposed to thefirst electrode and the layer comprising semiconductor nanocrystals isdisposed between the two electrodes and in electrical communicationtherewith.
 22. A device in accordance with claim 19 wherein the deviceis a light-emitting device.